IMO Debian is by far the saner distribution these days and there’s no reason at all to use Ubuntu for most people.
You mean Debian stable. But you have a choice, you can select testing or unstable, which gives you newer software.
There is no real need for "ancillary package managers", and all they do is complicate system maintenance.
Anyway, using Guix, Nix, or Flatpak is definitely a better idea than installing standalone debs for a different version of Debian than you're running, where it may be built against libraries that aren't part of your distro.
If you want to use the Debian package from Sid on Testing, better to rebuild it from source. openSUSE's public instance of the Open Build Service is a convenient way to manage keeping a repo for that up to date. But that definitely complicates system maintenance, too!
Only if you assume new bugs are better than old.
https://www.mozilla.org/en-GB/firefox/all/#product-desktop-r...
Can you please give an example of an application you needed available only as a snap?
Which might be fine! If that's the kind of system that works for you.
~$ firefox -v
Mozilla Firefox 102.5.0esr
I guess I don’t want up to date browsers.