It's a key difference IMO, and the main reason I like forums and heavily dislike the twitter-style apps. I want to read the voices of many, not the voices of few "influencers". You can make it look like a forum, but it's still gonna be focused on the voices of few.
That being said, with reddit going crazy over the last few years (and especially this last election cycle), I'm open to suggestions on new places to try that focus on forum-style discussions.