That's not my experience. I routinely get a polite "that might not be the optimal solution, have you considered..." when I'm asking whether I should do something X way with Y technology.

Of course it has to be something the LLM actually has lots of material it's trained with. It won't work with anything remotely cutting-edge, but of course that's not what LLM's are for.

But it's been incredibly helpful for me in figuring out the best, easiest, most idiomatic ways of using libraries or parts of libraries I'm not very familiar with.

I find it very much depends on the LLM you're using. Gemini feels more likely to push back than claude 3.7 is. Haven't tried claude 4 yet

Ask it. Instead of just telling it what you're doing and expecting it to criticize that, ask it directly for criticism. Even better, tell it what you're doing, then tell it to ask you questions about what you're doing until it knows enough to recommend a better approach.

This is key. Humans each have a personality and some sense of mood. When you ask for help, you choose ask and that person can sense your situation. LLM has every personality and doesn't know your situation. You have to tell it which personality to use and what your situation is.