Huge mistake on my part, avoid reading this post, as it is incorrect. The answers to the op have some value nevertheless.
Let us consider for a moment the Medium armor master feat. It allows you to be stealthy in any medium armor (wearing medium armor does not impose disadvantage on your stealth checks) and it also lets you add +3 instead of +2 to your AC, if your dexterity score is 16 or higher.
So the first part of the feat allows a stealthy character (who values his stealthiness) use a scale mail instead of a chain shirt when starting the game, and later on when the character has enough gold to upgrade his/her armor, the feat allows said character to use a halfplate instead of a breastplate. That essentially is equivalent to a +1 to the character's AC.
The second part of the feat is much more straightforward, basically allowing a character to add +3 to his AC (provided his dex is greater or equal to 16) instead of +2, which is the case with medium armors. So, this can be sumed up to another +1 to the character's AC.
Hence, the benefits of this feat can be sumed up to a +2 bonus to the character's AC.
Thematically, the feat looks just fine, and seems to be the ideal choice for a stealthy character who just wants to add a little bit of tankiness to his repertoire. That was at least what I thought for my human dexadin when I created her. Choosing this feat at 1st level raised my AC from 17 to 19 (halfplate as we started rich enough for 1st level, and mariner fighting style), so I was pretty happy that I could act as the secondary tank of the group when needed. But how important really is that +2 to AC that this feat grants. How much tankier does my character get?
Let's break down a bit that +2 bonus to AC. Basically, +2 to AC means that I reduce all incoming damage from attacks that target my AC, by a 10% percentage of the average damage that those said attacks deal. So if I fight against an enemy who every round tests my AC, then that +2 to my AC means that the enemy is going to miss one additional time on top of what he would have for every 10 attacks he makes, so that can be viewed as 10% less incoming damage per round. But what does this exactly mean? Is it better than for example having some more hit points? And if so, how many extra hit points would be preferable to this +2 bonus to AC? This depends on a lot of factors, but with a few simplifications, we can answer this question up to an extent, and hence determine the usefulness of this feat in terms of numbers.
Consider a campaign where all fights are against enemies that target your AC. There are no attacks or spells that test your saving throws, everything that is out there to get you, will have to beat your AC in order to hurt you. By assuming so, AC is suddenly much more important, and that +2 bonus to AC that the feat grants you looks to be the difference between life and death for your character. I make this silly assumption, because even under these circumastances, the feat is redundant imo. Now let us consider the maximum amount of damage that this feat can prevent for our character, on an average basis. Since the +2 bonus to our AC equals 10% less incoming damage, and since a character can only take so much damage as his maximum HP, this +2 bonus to AC is equivalent to an increase of your total HP by an amount equal to 10% of your maximum HP. And this is the case on the worst case scenario, when the battle is so difficult that you eventually will drop unconscious (but hopefully you stood your ground enough for your allies to claim victory and stabilise you). In every other case, when a fight is not that hard to drop you unconscious (or at least bring you thereabouts), the +2 bonus to your AC is equal to less than the amount I said before (and that was 10% of your maximum HP). But let us consider the best case scenario for the usefulness of this feat (which may be oddly a bad scenario for the character having the feat), in which scenario the feat benefits us in a way (+2AC) which as I said is equivalent to having an extra amount of HP equal to 10% of the character's maximum HP. So for example, for a character with 30 hp, the benefits of this feat can be broken down to raising the character's maximum HP by 3, to a total of 33. For a character with 50 hp, it's 55, for a character with 100 hp, it is 10 more, so 110, and so on.... And that is under the hypothesis that all attacks target your AC and that the battle is very very hard. Taking away any of these two conditions, the feat becomes weaker.
Let us come back now to the point that we needed to pick a feat for our stealthy character, that would add a bit of tankiness to him. And say that we pick the feat Tough instead, which gives us 2 extra hp per level. Lets make a comparison of those two characters, who are the same in every other respect, except that the one picked the Medium armor master feat, and the other picked the Tough feat, and see who can tank better.
In order to maximize the efficiency of the Medium armor master feat, I will assume my 2 previous conditions (that all attacks target my AC and that the fight that tests those 2 characters is so difficult that it will drop them unconscious), and furthermore, I will assume a d12 HIT die and a Con score of 20 with which our character starts play. All these conditions act in favour of the medium armor master feat, but do not affect the benefits of the Tough feat in any way. We will refer to the character with the medium armor master feat as character A, and to the character with the Tough feat as character B. So, at first level, character A has 17 hp and the medium armor master feat, which is equivalent to having 17 + 1.7 = 18.7 hp. And character B has 19 hit points. So character B is tankier at first level. Leveling up, and assuming no feats, both characters would gain 12 extra hp. Hence, for every level up, character A gains 12 + 1.2 = 13.2 hp, while character B gains 12 +2 = 14 hp. That makes the gap even greater as the character advances in levels, in favor of the tough feat. So, even in a campaign where every attack targets your AC, the medium armor master feat cannot match the benefits of the tough feat. And since the purpose of this feat (medium armor master) is to make your character a bit tankier, why would anyone pick it when there is no prerequisite for picking the tough feat whatsoever?
I know that someone could say something that has to do with the bounded accuracy system and how it all works, but honestly, bounded accuracy does not affect in any way what I described here, nor does it bump the medium armor master feat in some way that I failed to mention. Numbers do not lie. The only obvious benefit of the medium armor master feat to the tough feat, that I did not mention so far, is that if our character plays with concentration spells, then having the medium armor master feat will let him roll one less concentration check for every ten of those. So, when the character with the tough feat will have rolled 10 concentration checks, the character with the medium armor master feat will have rolled 9 concentration checks, hence the character with the medium armor mastery feat will have the tiniest advantage of maintaining his concentration spells over the character with the tough feat. Healing that you recieve during combat, acts slightly in favor of the medium armor master feat, but honestly, the difference between the effective hit points of the character with the medium armor master feat and the hit points of the character with the tough feat is so vast, that it does not make an actual difference. Bottom line is, that even with those ridiculous conditions we took into account (and which all favor the medium armor master feat), the tough feat is simply strictly better than the medium armor master feat. And that is my definition of redundant.
Having all this in mind, now consider the comparison of those two feats in a normal campaign, where AC is not the only defense that your enemies can test. Not to mention that not all battles are going to be extremelly difficult (which acts in favor of the medium armor master feat, as it maximizes its effect), nor will your character's con score and hit die will be 20 and a d12 respectively (which again favor the medium armor master feat over tough). The term redundant now feels as if it was a kindness on my part.
When I started writing this thread, my purpose was not to ask for ideas on how to make this feat worth picking. But since we managed to get here, I ask those patient enough to go through all my bad structured analysis and arguments, to hit me with your best suggestions.
The simplest way to infuse some sense to why this feat (medium armor master) even exists, would be to set a requirement to the tough feat (perhaps a high enough constitution score). That would let stealthy characters that want to add a bit of tankiness but dont have necessarily a high enough constitution score to achieve it by picking the medium armor master feat. It would still be worse than the tough feat (significantly worse imo), but it would be their only choice (not taking resilinet con into account, say we assume an even con score so that resilient con wouldnt make a difference) to add that bit of tankiness they wanted. Hence there would be an uncommon yet logical reason, for the medium armor master feat to exist.
But since making the players' life more difficult (by adding homemade additional requirements to feats) can never be the answer to anything, adding something extra to what the medium armor master feat provides a character with, might be the answer to why this feat takes some precious space in the PHB. What could that potential 3rd bullet under the feat description be?
Sorry, you lost me about a third of the way through. You got some things wrong and were already taking WAY too long to way what you wre trying to say. Shorten it up and I will be willing to go into more detail about why your damage analysis is wrong.
I figure the real reason that it's redundant is that it's primarily useful to dex based melee types, who are probably better off getting a Dex increase in the long run.
The +3 dex modifier AC is only really useful to characters with an Dex Score of 16 or better. Given a standard point buy character they'll generally only have one of Dex or Str to focus on. So a strength based melee character is probably not going to choose it, since they most likely have a low Dex and heavy armour, A Dex based melee character is also unlikely to choose it as they'll want to get their Dex to 20 for accuracy reasons, and can then choose to wear studded leather for an AC of 17, which is only a single AC point behind the maximum of 18 mith Medium Armour Mastery.
bid wrote:
Corran21 wrote:
I know we're supposed to ignore this now, but here's my take on things:
Even with a Dex of 20, going from studded leather to half plate and medium armor master would provide a +1 bonus to AC (12+5 is 17 for Studded Leather; 15+3 is 18 for Half Plate). So a dex focused Ranger might get value out of it, especially if AC is really important to them.
There's also a pretty small corner case that makes MAM a pretty effective feat. That's any sort of multiclassed Rogue grappler. They want a high STR to use when grappling, so you can make that your attack stat. But you need DEX 13 to go into Rogue, so you might as well have a 14 DEX to start and use Medium Armor. You stop at Breastplate if you want to avoid disadvantage on Stealth checks, unless you take MAM. Now you're quiet and as hard to hit as someone in Full Plate. Particularly good with Fighter/Rogues, as they get a ton of ASI's, letting them spare one for this admittedly marginal feat.
Barbarians are stuck in Medium Armor, have only STR as a stat to max, and might possibly care about stealth. They make pretty good possible users as well.
MAYBE on a single class Land Druid, but who does that? 
FabulousRex wrote:
There are magical nonmetal armors, dragon scale and other such.