You just had a very bad experience because you are already very tech savvy.
Breaking with upgrades or needing an at least medium savvy user to do them
- That's why they advise to set up Timeshift ON THE FUCKING SETUP. As for the updates, it notifies you when you need to and you should.
lacking behind on updates
- That's why PPAs exist. Besides, the average user is NOT interested in bleeding-edge software.
incompatibilities with ubuntu that may occur
- Ubuntu is not recommended anymore. Also, there's LMDE for that purpose.
Upgrades not being enforced-ish so noobs don't care and don't upgrade
- Updating your computer is YOUR choice, it's YOUR computer.
flathub being preinstalled but only verified apps are there, instead "unverified" deb packages are promoted
- The App Store (or whatever it is called) includes BOTH OFFICIAL deb packages AND VERIFIED Flatpaks.
desktop looks ok but kinda ugly
- There's XFCE and MATE editions to solve that. Even if those DEs may not be enough, you can install a new one.
apps same, subpar to KDE
- Atleast they're more beginneer-friendly. Also, there are the two other DEs' apps and installing s new DE if they do not like the current one. (Very unlikely, because most pc users come from Windows.)
X11? I hate when people like LTT think that this outdated stack is what we currently have on linux.
- There's a "Cinnamon on Wayland (Experimental)" session for that. And also, installing a new DE.