Technical stuff aside, a major reason why Flatpak does not get the hate Snap does is because users don't resent it.
There are 2 things people hate: the way things are, and change.
Ubuntu put Snaps on users desktops without asking if they wanted them. They just did it, then closed off ways to opt-out/avoid them (Cf. Firefox).
Forced change fosters resentment.
No distro made Flatpaks default/required/opt-out. Users had time to come to the tech and adopt it on their own terms/needs.
Just IMO.
@omgubuntu There were technical reasons behind the decision to move web browsers from debs to snaps, as it greatly reduced the maintenance burden.
As a worst case, imagine the period just after an LTS release has come out, and you need to put out a Firefox security update. There's two other supported LTS releases, and the previous Ubuntu release still has a few months of support left. Each of those releases builds for about 6 architectures. That's a lot of builds to push out.
It's also possible the new version of the browser doesn't compile with the compiler in the oldest Ubuntu releases, so it may need a compiler backport to build.
With the snaps, we just need one build per architecture that will run on all releases. Further more it can easily use the libraries and compiler from a newer release as its runtime, so less need for backports.
omg! ubuntu
James Henstridge