For "reasons" (i.e. I got a job at SUSE), I have been running openSUSE for the last 6 weeks. I like that I don't have to deal with snaps and flatpaks at all. I was able to install Slack, VSCode, Chrome, etc... from professionally maintained repositories. Open source apps like GNote just install cleanly from repos.
That said, it's nice that people who prefer snaps or flatpak (assuming such people exist) have that option without those packaging formats being shoved at me constantly.
Gaming has finally gotten me into desktop Linux. Most of my prior exposure comes from occasional using remote VMs in a work setting, which are generally maintained by other people. That is to say: I don't have a lot of first hand experience with packaging/installing on Linux.
But my understanding is that Flatpak solves the problem of "this guy has Ubuntu and that guy has Pop! and they both want to download this app, but each distribution has its own packaging system." Having a stable target that works across distributions seems good for the ecosystem.
Or developers compile a static linux binary for the specific architectures (usual amd64) and just compile all of the dependencies into the app. You download the binary and run it. That used to be how Steam worked, for example, and I assume still does.
I think that what snaps and flatpaks want to do that is "better" than this, is to isolate your system from such applications if they are malicious.
Your description of Flatpak is technically more apt for AppImage than Flatpack.
What you said is not wrong, however, it misses the bigger picture because like Snap, Flatpak also includes a package repository and distribution mechanism, whereas AppImage only solves the problem of running a dynamically linked binary on an unsupported distribution (the problem you described)
That said, it's nice that people who prefer snaps or flatpak (assuming such people exist) have that option without those packaging formats being shoved at me constantly.