My biggest gripe with Discord is with people using it for FAQs or help for their communities. Search engines cannot index it and you have to sign up to see anything there. It's very annoying to join a server, ask a question only for someone to just type "!faq" and have a bot reply with an FAQ post. Why not just have that somewhere else?
It's not really Discord's fault but I also don't see them trying to do anything to alleviate the problem (why would they, more users is good for them). Are "forum-like" tools that difficult to set up? Even Reddit allows people to create subreddits easily. That is a much better solution in my opinion. Is it just that they're already familiar with Discord so they use that? That's my gut feeling.