Indeed, joining a Libera channel from Matrix is as simple as joining #channel:libera.chat. It’s much simpler and cleaner than the Freenode bridge.

It's not FOSS (neither client nor server), you can't control any of the infrastructure (and therefore guarantee any level of privacy), sovereignty of the data, the data itself, and policies for use which may not align with your own.

All before you get into the technical differences in applications and protocols - good and bad.

The problem with proprietary chat services is that if, for instance, Discord pulls a Freenode you need to look for an entirely different app to migrate. With IRC or any federated network for that matter you point to a different server and its business as usual. See how fast everything moved over to Libera over the past few weeks.

The biggest issue I personally have with Discord is that everyone has a "server". And that server has 42 highly specific channels on it. And it has as many bots as Snow White had dwarves.

...and it has less users than channels.

Discord should have a "lobby" server where every small group could have a (private, invite only by default) channel. After they have enough people they could upgrade that to a full server.

But it's too late now and I already have 50 Discord servers on my client, of those maybe 4-5 have over 50 people on them. The rest have more channels than members.