Flathub aims to be the place to get and distribute apps for Linux. It is powered by Flatpak which allows Flathub apps to run on almost any Linux distribution.
How does it stack up against traditional package management and others like AUR and Nix?
purely as an end user i hate how much it downloads with each update and how much it uses the disk space although that's much less of an issue. i know it's solving a real problem and relieving a lot of the headaches of developers maintaing packages for each distro's specific package standard, but it's simply not the software distribution solution for people without at least well enough internet.
i wouldn't use any distro with flatpaks as its main way of delivering software and i would in almost all cases always choose alternatives even if it's outdated. i don't necessarily hate flatpak itself but for me i don't want to spend money on extra data cap and wait 30 minutes for a small update for my game launcher to finish.
the appimage of one of the applications i was interested in was 3 times less than the average flatpak update so redownloading the appimage every time would be better. if i installed more packages yeah the math would be better but it's still wasted data per update no matter how small it actually is. i found out after a while of using flatpak that i wouldn't just update and was stuck with outdated software anyway.
the actual update size for the application is logical as far as i remember, it's the other stuff alongside it (i think related to graphics card) which is the real issue. it added around 500MB each update while the actual update itself might've been 10 or 20 MB.