To be fair that takeover was only possible because the owner of freenode sold the server to a malicious party which is only possible because you own the server, so that kinda reinforces parent's point.
As a freenode user I have no say over who the freenode owner is, much like I have no say over Discord's moderation policies. It's the same puppet with different masters; neither situation really empowers me. Yes I can always start my own IRC server but if nobody wants to join it what's the point? 99% of the battle is getting people into the same virtual room.
You usually own the domain, unless you sell out of course. So you can start wherever you want from scratch on your own or on leased infrastructure. People will connect to the domain/irc network.
I'm not saying you should use IRC over Discord, but hey, that's how the web got centralised and why certain platforms have lots power: because people just gave it to them. If Discord decides to monetize by leveraging ads, good luck to you and your community.
You don't truly own the domain though. You rent it. You have to continually pay to maintain control over it. It also wouldn't be hard for the registrar to claim you violated their ToS and revoke your access to the domain (or if they don't think they can get away with that, then they can say that they failed to process your payment when the domain renews and then snatch it up instantly themselves so you can't get it back).
Yes you have to continually pay pizza money, yearly, true. Rent a country level domain and it won't be revoked without a judicial order. Also rent from a registrar with good reputation.
I don't know what a self-hosted service that lets every user have power over the instance would look like, but the original argument was that IRC gives you ownership over your own server.
Hell, the "no say over the owner" argument isn't even restricted to self-hosted services, there have been numerous cases of a discord admin nuking the server over some petty drama.