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.