Very bad is pretty harsh for the possibly least bad chat app that I have used. I don't like the centralization on Discord but the reason it is popular is because their app is better than the competition.
replyimo Telegram is the least bad chat app that I've used. Discord has a lot of UX and performance issues.
replySlack is a very bad that is super slow no matter what time of day I use it. It completely locks up on a spotty network. Discord works way better and their voice chat is several leagues above.
replyTry alternative, native, Slack clients like msga.app or similar. They tend to use Slack's API pretty efficiently.
reply