> legitimate questions being closed for no good reason
They are closed for good reasons. People just have their own ideas about what the reasons should be. Those reasons make sense according to others' ideas about what they'd like Stack Overflow to be, but they are completely wrong for the site's actual goals and purposes. The close reasons are well documented (https://meta.stackoverflow.com/questions/417476) and well considered, having been exhaustively discussed over many years.
> or being labeled a duplicate even though they often weren’t
I have seen so many people complain about this. It is vanishingly rare that I actually agree with them. In the large majority of cases it is comically obvious to me that the closure was correct. For example, there have been many complaints in the Python tag that were on the level of "why did you close my question as a duplicate of how to do X with a list? I clearly asked how to do it with a tuple!" (for values of X where you do it the same way.)
> a generally toxic and condescending culture amongst the top answerers.
On the contrary, the top answerers are the ones who will be happy to copy and paste answers to your question and ignore site policy, to the constant vexation of curators like myself trying to keep the site clean and useful (as a searchable resource) for everyone.
> For all their flaws, LLMs are so much better.
I actually completely agree that people who prefer to ask LLMs should ask LLMs. The experience of directly asking (an LLM) and getting personalized help is explicitly the exact thing that Stack Overflow was created to get away from (i.e., the traditional discussion forum experience, where experts eventually get tired of seeing the same common issues all the time and all the same failures to describe a problem clearly, and where third parties struggle to find a useful answer in the middle of along discussion).