I mean, many games have mechanics to make dungeon content more challenging in general.

In this case, I think earlier versions of WoW have a pretty good handle on things:

Monsters X levels above you can perform crushing blows, likewise your attacks can glance (or be resisted more easily).

The key thing to take from this is that tank builds would get a stat that reduced (and eventually nullified) the chance of a crushing blow happening.

In simple terms, PG could have a tank-focused stat that reduced enemy critical strike chances - but I'm still iffy on the concept of monster critical hits in general as it leaves a lot of your success up to RNG - maybe critical hits are the real casino?