I noticed all sorts of horrible breakage in Ubuntu (including LTS updates) over the last 3-5 years (I gave up on it in the 20.* days for anything except VMs / docker containers) Examples included DNS taking 5 seconds to resolve each host, the syslog fiasco, systemd flat out not working, etc, etc.

Maybe that's what they're referring to?

(At this point, I'm looking for anything that's stable and still uses a normal init + x11, FWIW. I wouldn't consider Fedora, since it's owned by IBM, and Red Hat's new business model under them is "systematically violate the GPL and see if we can get away from it".)

I have one machine with ubuntu 22.04, and I've never seen any of the described issues. I doubt that 23.10 regressed.

That's not really what I meant by modern

So, modern by your own definition of "modern". What is it exactly besides being Fedora?