I don't get this. Slack was made for small to medium teams. There's so many Slack chats are that unbearably slow (or expensive) because it can't handle that man

I don't get this. Slack was made for small to medium teams. There's so many Slack chats are that unbearably slow (or expensive) because it can't handle that many users. Also, I have to get invited, check my email, sign up, and skip the tutorial every time?