To a degree it's expected since an AppImage has less sandboxing and container overhead; but I don't think that your experience is necessarily universal, Flatpak and Snap are doing things like bundling updated Mesa drivers, GTK versions, Wayland protocols, audio libraries, and etc; looking at the Snap now, 15% of the users are still on Ubuntu 22.04 which is 4 years old; despite that they're running Joplin with GTK and GPU drivers from 2025. There's 100 users doing that on 18.04 even.
KDE is awesome and Fedora is too, however I think it's fair to say that KDE became much more recognizably awesome with KDE 6 release about 2 years ago; and until then might not have been treated on par from devs and users compared to Gnome. Even by Fedora itself, "Fedora KDE Plasma Desktop", the official release as opposed to the spin/remix, is only a year and a few months old. (I think)
But I'm happy Fedora pushes KDE, because the combination of the two is fantastic. You might similarly like to try e.g., Kubuntu if KDE is your thing, where you'd then be able to compare the base distribution layer (Debian/Ubuntu vs Fedora itself) vs the graphical layers, but ultimately, they're more similar than different except where you might be exposed to requirements like e.g., running an application server at work on them. Businesses would be fine with Ubuntu Server, but I've never seen anywhere happy with Fedora Server due to the more rapid lifecycle (this is ignoring RHEL/CentOS/etc, which are built on Fedora - enterprise loves those). If you're happy with Fedora though as you are now, you could easily run it for years, it achieves what it aims to be brilliantly and is in many ways ideal for home users in professional capacities too.
Fedora has an excellent reputation for security and I would say amongst the best in the general desktop Linux distributions by default, putting significant effort into things like e.g., SELinux, pushing Wayland super early, having robust package building transparency standards & etc.
Red Hat the business also has a good reputation in Linux. They've contributed massively over 30 years. Anytime money is involved some people will start spouting nonsense ignoring the reality that Linux is both a community and commercial endevour at the same time, like any company there can be dramas, but put simply, if you can't trust Red Hat then we're all screwed, basically.
This sounds to me like maybe you've new or niche hardware and there's been updates to the kernel or driver stack; Fedora is fairly aggressive in upgrading these to the latest versions moreso than e.g., Ubuntu which does the same via "HWE" releases but with a longer delay - which can be the difference for some people between works great and not working at all. (& which would impact the snap stability for example, since it uses Ubuntu, and the Flatpak, since the runtimes are separated to the system but I'm less sure their release cycles).
Let us know your experience on Github, in the six years I've been helping out Pinta, it's been mostly a very small collection of people working on it and at one point was basically a single person doing 99% of all the work. It's healthier these days, but I think Pinta has like 3x more Linux users than e.g., Joplin does but gets significantly less engagement. It isn't some big thing with active devs work but people using the tool to make it better for themselves and others in their spare time. There's genuinely a lot of valid feedback that people are happy to post on Reddit & etc but never actually gets seen by the people who might be like "Oh that's so obvious, you're right actually!" - that isn't me saying everything can be taken on, but as one of the people helping out with it, you'll begin to see that sometimes it's a small world in many ways yet huge at the same time (I do the Joplin & Pinta snap too to be clear, and some nicher stuff in Pinta itself outside the Snap bit from time to time).
Edit #5:
HELLO AGAIN! Didn't realise this was you 