Discourse is perfect for communities and basically the best forum software out there. Wherever a forum would make sense, Discourse is probably the best solution. Having said that, small corporations with little external outreach have limited advantages with Discourse, since it's designed to facilitate discussions which happen at a slower pace while startups and small corporations will probably want to move faster with software like Slack.
Vanilla's mobile functionality was downright awful and it felt like it was stuck in the 2000s. While they have similar features, Discourse blows them away in almost every department. We don't regret switching at all.