I want to believe this, but it's hard for me to take this at face value. It's been about 4 years since I've run pmOS, so my experience IS very out of date, but I also have a hard time believing that the experience has radically changed in the meantime.

The short is that yes the GNOME/KDE apps do often look more impressive, but they suffer the same sort of malaise which seems to have infected Linux desktops sometime since Eternal September, and between the sporadic crashing and "this doesn't feel right", it's really hard for me to accept "It's more polished than AOSP!".

pmOS's installation page opening with a warning:

   Make sure you read state of postmarketOS before installing postmarketOS. 

Which leads to a page that opens with:

  The goal is to make postmarketOS usable for everyone, but we are not there yet. Usability and most importantly stability issues need to be worked out first. If you are looking for an OS that is as usable as iOS or Android, this project is currently not for you.

Does not do a lot to dissuade my skepticism. I know you said the apps specifically, but even there, it's like... I dunno.