One of the things I notice in these discussions of what is an optimal choice is the relative lack of trade-offs. With respect to armor, there's cost, strength requirements, weight, and whether or not stealth is at disadvantage to differentiate them and offer any reason to NOT go for the best AC on the subtable you have access to by training. And both weight and cost are minimal factors since almost nobody seems to use encumbrance as a rule and PCs blow past the cost restriction quickly in their adventuring lives. All heavy armors impose disadvantage on stealth, so that's not a factor either. So why opt for chainmail instead of plate? Presumably because your strength topped out below 15. And that's IT. That may be a factor for a cleric who has proficiency in heavy armor, but is it really a factor for a fighter or paladin? Probably not. And frankly, splint armor might as well not even be on the table, right?
Unfortunately, basic pluses for magic armor aren't really a help here since they just shift the AC of the armor. And this is where D&D's evolution tends to work against itself. In several prior editions, magic armor's weight was ignored in calculating encumbrance or it stopped reducing movement rates. But those are functionally irrelevant in 5e. So why would anyone wear +1 splint armor when plate armor is available? The +1 splint armor is worth a lot more to sell, even with downtime rules, than wear.
