Slack it's more bound to Jabber than IRC.

IRC = public stuff, tech stuff, hackers. Yes, /query exists but it was mainly used to met skilled but unmet people together.

Jabber = IM, mostly private messaging with people you already knew. Groups where just built from people with close friendships, and, yes, often it would be made from IRC.

But, now, Slack and Discord try to do all (even a replacement from forums), and, worse, with propietary protocols and silos. If Discord dies, say goodbye to your content. Forever.