You are very much talking about late era StackOverflow there.

What marked it out originally (and was visible in some other less-travelled StackExchange sites rather later) was a culture of holding replies to a sort of account in the reply comments; people urging each other to make their replies better-sourced, less hollow, more responsive.

The goal of being non-duplicative alas ultimately is always going to lead to a culture that polices itself too hard. I am an LLM cynic but I think it’s possible that LLMs could actually help steer that process more gently, guiding submitters to likely answers but also helping them fine-tune a more specific, narrow, never-asked question.