This is my issue with systemd. I wanted Linux because I wanted to have a choice. The philosophy was that users should have a choice. Systemd goes against that: it's taking over everything and more and more projects require systemd. Flatpak as well: if a project only supports flatpak, chances are that it won't be easy to package normally. So if I don't use Flatpak, I'm screwed.
People who don't see the problem with systemd "because it works" miss the point, IMO. It's like those devs who proudly ship their project in a docker container, because they are not capable of making it properly available to package maintainers. "It works", but I can't package it for my distro because it's a big mess. Developers don't have to package their project for all distros, they just have to properly provide the sources. But more often than not, they don't know how to do that, and instead see Flatpak/docker as "good alternatives that just work".