I have played with using FlatPak, and while it seems snappier than snap, I always ended up with something not quite working, because of permissions or sandboxing. The answer to a lot of problems seemed to be "don't use the FlatPak version".
The set of software I use complex enough to need something like FlatPak while also not needing to interact with other things is basically very, very small.
Snap _was_ a bit slow in the early days. It's not any more.
I use Ubuntu 22.04, 24.04 and 25.04. Snap is pretty fast these days.
I have gone around purging all my custom repos and PPAs, removing those apps, and reinstalling the snap versions. It's just easier and it works.
I am running 3 quite elderly Thinkpads in near-daily use: an X220, T420, and W520. All Core i7, all with RAM maxed out, all with SSDs. They are perfectly usable for what I need and they have great keyboards which no more modern Thinkpads do.
Ubuntu 22.04 on a 13-year-old Thinkpad loads snap apps in an eyeblink now. I can't detect any delay compared to natively-packaged apps.
Yes, it uses a bit more disk space.
I used to remove all snaps and then `apt purge snapd` but it's not worth the extra effort any more.
Glad to hear they fixed the speed issues; I just moved to PopOS.