oh yeah, the ring does effect AC. didn't notice that earlier, my bad.
defense (the fighting style you're referencing) only works if you're wearing armor, so that gets nixed here, and again, very few characters are going to get to 20 in both of their unarmoured defense stats (monks have a better chance because they actually use dex, but i don't see most barbarians going past 14 dex and even that's only to fill out medium armor because, frankly, medium armor is just better then a barbarian's unarmoured defense most of the time). i'd guess until level 16-19 the actual maximum will probably be closer to 20.
again i think shields should get a total rework to make them more interesting then just "more AC", but like that'll ever happen.
yeah it's really not, you're right.
to be fair, at the levels you're going to have all of this set up, you're fighting things with like...+19 to hit, meaning even 25 AC is kind of a joke. the problem is not just player AC - bounded accuracy kind of just goes out the window after a point. it's EXTREMELY noticeable with saves.