The problem with LLMs as a replacement for StackOverflow (and any other peer reviewed Q/A site) is that the LLM has, shocker, no peer review. Combined with the fact that the user has insufficient expertise to adequately vet the responses (ie: they needed to ask in the first place), there is a trap where the user can end up using an incorrect response without any expert feedback to help them make an informed choice.
As the LLMs get better, I expect that this will improve, but for now, it's gonna train a lot of novices to apply bad practices.