everything is completely boring text, no images

You literally just listed some of the reasons IRC is better. That said, I don't see any reason an IRC client couldn't be made to support images, with the understanding that it would have to be done in a way that falls back to posting it as a link for people using text-only clients, but that shouldn't be too difficult.

can't message people when they're offline,

This functionality can be enabled on IRC servers or on a per-channel basis using bots.

it's not clear how I can easily setup my own server.

Again an advantage of IRC. Not every group of 2 people need their own server. And a simple 2 second Google search (or learning your IRC client) will show you how to create your own channel in seconds.

the discoverability with any IRC client tends to be in the negatives.

That really depends on the client. There are (or at least used to be) plenty of user-friendly IRC clients. How many alternate clients can I use with Discord?

And heaven forbid someone should have to think for more than 3 seconds when learning something new to them.

I swear I sometimes think that once all of us Gen-Xers are gone, there won't be anyone left who actually understands how the Internet or the technology that runs on it actually works, as prophesied by Idiocracy.