Zorin OS makes so many right choices in my opinion, especially as a serious alternative for normal people to recommend. But they are ubuntu based just like Pop!OS, elementaryOS or Mint.
Mint has LMDE at least and are pushing it pretty hard. Never used it as a daily driver but have heard that it is stable and fast.
I also use Debian Testing with GNOME and it works perfectly fine.
What does Ubuntu offer that Debian does not for so many Distros to build of. Is it extended hardware support? or is it just an historical choice made back when Debian was not a great choice of a base for whatever reason? I really do not get it. As a non-maintainer i expect it to be a nightmare to have an already heavily changed base to build on and Ubuntus choices in the past were also rather questionable.
It has newer packages than Debian. And even though Debian releases new stables every couple years, at least historically, it has kept old package versions around for way longer than that. Before I started using ubuntu sometime in the '10s, it was normal for a debian stable package to be upwards of 10 years out of date.
And it wasn’t like today where you have containers/VMs, PPAs, flatpak/appimage/snap/etc… if you needed a newer version of a package for whatever reason, often you couldn’t just compile it yourself or use the testing/unstable one because it had cascading dependencies that were also newer, so you were just screwed. Being able to have a “stable” release with newer packages was a huge draw for Ubuntu.
I can’t tell you how many installs I killed back in the day by dividing down the dependency rabbit hole.