The lack of familiarity with irc from slack only users seems to reveal an unfamiliarity with irc being a connected universe of many slack sites being on one network.
The Lounge is a web client, so you can access it from any browser (PWA, push notification support). Since your IRC connection runs on a server, roaming and connection drops is not a problem.
Ha ha that's crazy talk! Eventually they threw my IRC server off of EFNet because 8 total megabytes of ram for the server+OS was too little for the working set.
Newer is not necessarily better.