Steam Deck is weird. I mean, I love it, but coming from vanilla Arch it can be frustrating at times. Discover is terrible. Luckily, Distrobox is a thing.
I putz with Discover sometimes. Though I have no idea how it resolves package updates under the hood, as it often will produce a different manifest than running dnf itself.
I usually can't find what I'm looking for, so a larger catalogue would go a long way. I also had problems with some software versions. The one that comes to mind is that Firefox had behavior with the save dialogue that I don't like. It's a minor issue, but one that I don't have with the build in the Arch repo. I have a vague memory of something just not working, but I couldn't tell you what at this point.
Ah, I see! Yeah, a bigger catalog would be nice. You can add more repositories to it, enable Flathub, which provide more options, but something about it does feel hamstrung.
The Firefox thing is something I know about! You can set a config option in the about:config page to tell Firefox to use your desktop's standard dialogue. It has to do with XDG Desktop specifications, I think
It uses the system dialogue, but it starts from the same directory each time. If I'm saving files it's usually multiple files in succession, so I want the dialogue to start off pointed at the last directory I saved to. The Arch build does that.