IRC was here before Discord, and it will still be here after.
I've never heard of Stoat. Looks like IRC but it's Electron. Total waste of time.
For most Discord users IRC simply does not have the feature set that people need. Basics like simple drag and drop media sharing, threaded conversations, emoji reactions and voice comms, up to more complicated stuff like screen sharing and video calling.
IRC does not support group voice & video calls, which is one of the primary features of Discord (and previously Skype, from which everyone migrated to Discord in the first place)