Some projects have both a discord and an IRC channel and when you compare the two chats the conversations are wildly different — IRC being a more focused, on topic chat without floods of gifs, emojis, and off-topic channels.
The hardest part about using IRC is getting chat history and mobile notifications. As part of https://pico.sh we run a soju bouncer (soju.im) for our members to use to help with that. We have a bunch of daily active users.