I can share your experience that good web forums are really rare.

If you happen to speak German there are two that I can recommend, though

The German debianforum.de is rather good. I only used it a few times yet, but most threads that I skimmed over contained rather good answers.

There's a (comercially driven, but not very ads bloated) general purpose forum called wer-weiss-was. It has a huge list of topics to discuss, and in some of these topics you can get really competent answers. For example you can ask about Mathematics, Physics, Astronomy and Chemistry, if you want at University level, and you'll usually get very good answers. Some of the computer and programming topics are also quite good, but they can't reach perlmonks standards.