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flatpaks as its main way of delivering software and i would in almost all cases always choose alternatives even if it's outdated.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 i found out after a while of using flatpak that i wouldn't just update and was stuck with outdated software anyway.