I'd counter that point though, and say 'then you should be/stay on topic' and not forking the discussion into other topics. It's certainly not difficult to create a new topic about a related discussion, and if it interests the original posters then yay, they might join in, but either way you aren't cluttering up the original discussion.

I see forums as more... professional? Whereas layouts like we have here are much more 'lol memes'. The two types serve two different users.

I spent a good chunk of my teen years on forums and it was definitely a direct, 'here is A Thing and I want to discuss A Thing' conversations. Lemmy/reddit comments are like 'I have this one thought of a kinda-tangible idea for A Thing 2' and it's just... It's not 'bad', but it's most definitely scatterbrain thoughts, just shared for other wandering thoughts to collide. Scribbled brainstorming vs careful planning, I guess? I dunno.

Maybe I'm just old. Blah.