>I can think of several humanoid non-dragon mobs that destroy
>gear. Are these affected by the change as well?

Depends. If it was with blast of fire, frost, etc. then the answer is probably yes. If they're busting weaponbreaker on you, then the answer is no.

>What about acid attacks that, while they don't destroy, do
>"etch and pit"? Do they no longer have that effect?

They don't; at least, not those coming from black dragons or similar effects. Rooms or digestive tracts that are full of acid remain as-is. Note that in addition to pitting and etching, acid dragon breath could also destroy certain kinds of gear, which it no longer does.