Speaking here as an art noob who generally knows nothing of what the pieces are supposed to mean or what their societal context was when they were made and what forces they were pushing against etc:

When my arty partner drags me into art museums with huge abstract modern art pieces with just big splotches of heavily textured color (I’m thinking in particular of one giant piece filling a wall with jagged black heaps of paint) they do in fact make me feel feelings.

In my case, as in OP’s case, they were really bad feelings. I would prefer not to feel really bad and I don’t like that art. But I certainly couldn’t call it ineffective fart-huffing!

Say it however you want that works for your relationship.

What I meant to be saying there was — if nobody tells him his review comments aren’t helpful anymore, then he probably won’t know.

I’m speaking from the perspective of somebody who spends like 1/2 their time or more doing code reviews, if I’m wasting people’s time I would want to know it

You need to tell him that. Seriously. Pick some especially bad example to point at, and come to him with, “Hey Bob, I used to get real value from your review comments. I could tell you were thinking about what to say and it helped me to produce better code. Now it seems I am mostly seeing LLM-generated junk like this one that doesn’t help anybody. This isn’t an improvement, can you go back to the more helpful way you used to do things?”