From my experience, most of the popular proprietary ones (think: Slack, Discord, Spotify, whatever) are distributed both as a flatpak and as a snap, while more niche desktop apps are usually flatpak-exclusive (out of those options).
Perhaps you just don't use that many things that aren't really popular or well known? I can't find PuTTY and KeePass (though obviously there are alternatives in those cases), applications that both have Linux versions and that I use every day (and aren't even that unknown).
Also, unfortunately the limitations of Flatpak mean even if what you want is there, say Wireshark, it often won't have full functionality because it is impossible to give it the permissions it needs. In Wireshark's case, it can't actually capture any packets. If you want to actually use it you'll still need to resort to a different installation method.
That being said, unless the flatpak has some features your distro version doesn't, for trusted software package is always preferred.
Flatpak is really for untrusted software/proprietary and projects that update with new features often.
For me this was a much bigger issue when I was on Windows, but also in Ubuntu which groups programs together similarly to the Windows taskbar. I'm on i3 now mostly and just use a normal terminal for ssh, but for quite some time I was using putty on linux specifically for window management.