Snap? It is fundamentally broken and Canonical shows zero interest in fixing that. Instead they try to patch applications to not be as awful when running via Snap.
Firefox is the best example, its a big application and suffers greatly from taking forever to start on Snap because of course the filesystem image is compressed, so it needs to be uncompressed, mounted and then firefox can start which is still slowed greatly due to snaps poor I/O performance.
A unpatched firefox took 30 seconds to start on Snap, they patched it to load only one language pack and some other small things, and now it starts in incredible 15 seconds.
Which is shit poor compared to the native firefox starting in one second and the flatpak starting in also one second. All on the same machine.
Snap is by far the most cruel joke out of canonical.
Flatpak has no such problems.