I'm incredibly cautious about awarding defense items.
Offense is much less of a problem - there are always more goblins and dragons than the party can handle.
But stratospheric AC? Not a good idea.
I suggest to everyone to hold off the plus AC items until at least third tier.
At double-digit levels, it feels more okay if ordinary foes like thugs and Orcs can't actually hit you except on a 20.
None of the PCs in my campaign (levels 11-14) are anywhere near 'only hit on a 20', despite defesive items:
Thuruar, warpriest Cleric-12 has +1 plate & shield for AC 21, recently improved from AC 18
Hakeem, barbarian-14 has CON 20 DEX 14 & +1 shield for AC 20, recently up from AC 19
Rey, Rogue-12 has DEX 20, ring of protection, and a +1 mithril chain shirt that stacks
with his DEX - so equivalent to +2 studded - for AC 20, recently up from AC 17.
The PCs didn't feel underpowered with lower AC (3 pts lower in 2 cases) and they don't
feel overpowered now. Most foes have around +4 to +7 to hit so are hitting on a 13-17.