This is quite possibly one of the most ridiculous arguments we've had here on ENWorld... worrying about a
single point of Armor Class at some higher level of the game with some strained set of circumstances all in an effort to do what? Change the armor table by adding in a new medium armor, just so the chart is somehow "balanced?"
You've got to be kidding me.
That single point of AC in this white-room simulation means
absolutely nothing. Because when you actually sit at the table,
none of your PCs are ever going to *be in* this very specific set of circumstance that makes this "addition to the Medium armor table" for balance reasons a requirement. Either someone will have the Defense fighting style and screw the balance up. Or someone will cast
Shield of Faith and screw the balance up. Or the necessary classes needed to show off this "balance" won't actually appear at the table together and thus screw the balance up. Or someone won't use their ASI's "correctly" to set up this arugment in the first place and screw the balance up. Or someone will use a shield. Or someone will get magic armor. Or use
Barkskin. Or cast
Pass Without Trace and make the "disadvantage on Stealth checks" no longer an actual detriment to the group. You are
never going to get everyone's classes, DEX mods, ASI selections, and the specific level requirements all lined up (without all the other AC modifying things) so that the players will actually reach that point and then sit there comparing their PCs and say "You know... something's not right here..."
This is the hallmark of why "white-room analysis" is in my opinion completely stupid. Because at
no point does the best-case-scenario of getting all the moving parts lined up to show off how exactly balanced you were somehow able to make the game,
ever actually occur. And even if in the most impossible of situations IT DOES somehow occur... no one sitting at the table and playing will actually give a hoot! Once the game starts, you have an AC of 14, I have an AC of 16, you have an AC of 19, my attack bonus is +5, yours are +4, that person's bonus is +5... everyone just has numbers on their sheets, everyone rolls dice that screw up the results anyway... and the way the d20s roll end up having
so much more impact on the results of the game than ANY attempt at balancing the niggling +1 over here for this thing and the -1 over there for that thing.
The game doesn't care about that +1 "imbalance". Players don't care about that +1 "imbalance". Players won't even recognize that there *is* some "white-room analysis" imbalance when they are playing because it is
impossible to comprehend how that 5% change from that extra +1 ever actually effects them. All they'll know is that when the d20 gets rolled... sometimes they get hit, and some times they don't. That's it. That's the end of it.
So if you want to add a new armor to the chart, then just do it already. But let's not fool ourselves into thinking it's ever going to actually matter.