What are developers supposed to ship their apps with? Make packages for every Linux distribution under the sun? Flaktpaks and Appimages solve a real problem. The current alternative is NOT being able to use the specific software at all because you don't have the right version of Ubuntu.
Maybe Guix/Nix are solutions for some of the pain points of traditional package management. And yes, libraries really need to focus on backwards compatibility. In the meantime, AppImage/Flatpack gets the job done. I am not out of luck when my distro does not offer the right package with the right version.
Yeeh, who enter the plateau, abandon all hope you will get away with leaky abstractions.
Wish the lazy bloat-load was build as architectural pattern into apps. It only installs when you actually use it.
This being said, I do see these systems that basically just double down on adding layers for layers' sake as more disruptive than systemd.