I have also seen bad duplicate closures that weren't actually exact duplicates. But people talk like this is the only kind of duplicate closure that actually happens. I've no idea if the rate of bad duplicates is so much higher than I observed, or if people are missing that their question is actually answered in the duplicate.
SO was a really rewarding place to ask and answer questions in those early days. It really is a crying shame what they did to the community by empowering the worst of the community to be the bosses.
The point is who decides. If you ask a question and I flag it as a dupe, I might think the answers on the other question apply to yours, but only you know whether they solved your problem or not.
> I've no idea if the rate of bad duplicates is so much higher than I observed,
Sure, and neither does SO! They didn't even measure it. They only looked at the signal "does somebody with points think these questions are similar", and discarded the signal of whether the new user got any value out of the site, and I think that's what did them in.
Sites like Quora don't have good moderation (nor social media sites) and they become less useful for "how do I do X" questions.
LLMs do the moderation of the underlying source and just give you the answer.