I think it can be useful for complex questions, but in my experience most of these discord servers are full of people asking very basic questions and very jaded people giving incredibly rude and cynical answers
And the people asking basic questions probably don't want to be asking anyway. I know from my days on the arch forums you will alway get basic questions even when the manual is exhaustive, but I see so many discord communities where the documentation is woefully incomplete, and the result is predictable: a constant flood of basic questions.
And the people being rude about it have created their own frustration. They picked a bad platform and are mad about how it's going. Further people who aren't deeply involved see what a bunch of jerkasses the community maintainers are and just disengage.
True, that would make it better to find the answer. My experience with traditional forums though is that I have to sign up to a brand new website and make a post only to not get a response, and because it's a brand new site I have to keep checking it for a response every day.