ICQ having more features than Slack isn't really a point of contention, ICQ could do about a zillion things.
I like ICQ. I used it. But I really just don’t agree it had “more” features. It had _different_ features. And those features are just kinda wildly different because of how business and the internet had changed. I just really do not think it is a useful point to try and imply is a weakness of slack somehow.