As Linux Audio user I have installed and tested various versions of Linux and tried a variety of applications. I currently use Debian Buster as my OS of choice for Audio Production with KDE Plasma 5 as the desktop environment, so there may be a bit of a bias involved. However I have chosen Debian for its stability above all else, and that it and its derivatives are the most popular Linux distributions. Along with using Debian, I have also added the KXstudio and Librazik repos which offers a plethora of Linux Audio applications and plugins. The list provided by having these two repositories is considerable. I also tend to build a lot of apps and plugins locally which allows me to be on the cutting edge of the Linux audio community. On top of that I have licenses for Bitwig, Renoise, Redux, Waveform 10, Reaper, Mixbus 6, DiscoDSP Bliss, DiscoDSP Vertigo and u-he ACE. 10 years ago Linux for audio was tedious, Today with the abundance of FOSS and proprietary software (Bitwig and Reaper’s inclusion in the list are game changers for my needs) Linux is where I had hoped it would be when I first installed Red Hat 6.
When looking at the top 15 distributions according to DistroWatch.com the list in order is
MX Linux Based on: Debian (Stable)*
Manjaro Linux Based on: Arch**
Linux Mint Based on: Debian, Ubuntu*
Ubuntu Based on: Debian*
elementary OS Based on: Debian, Ubuntu*
Zorin OS Based on: Debian, Ubuntu8
Fedora (Red Hat, RPM)
deepin Based on: Debian*
KDE neon Based on: Debian, Ubuntu*
antiX Based on: Debian*
Pop!_OS Based on: Ubuntu, Debian*
ArcoLinux Based on: Arch**
Of the 15, 11 are Debian derivatives. Add to that the 4 most popular Audio distributions/repositories all use Debian derivatives; UbuntuStudio, KXStudio, AVLinux and Librazik.
In the list above, 3 are Arch based, and for all intents and purposes the Arch community has had success porting Debian applications to their ecosystem.
The other consideration is Desktop Environment. My personal experience is that applications run on any DE. All that is required is to install the requisite Qt and GTK dependencies.
Of the 4 major Linux Audio distributions:
UbuntuStudio uses XFCE which is built using GTK+
Librazik -> Mate -> GTK+
AVLinux -> XFCE4 -> GTK+
KXStudio apps are built using Qt
Qt desktops can run GTK apps and vice versa, so even though Linux is not a Desktop, in my experience, having used Mate, Cinnamon, KDE and XFCE, most if not all apps can run under any DE.
My personal choice for audio is to stay as far away from Snap or Flatpack packages for reasons you mentioned above, but also that in my understanding these are background services. My preference is also to use a built binary over AppImages. For audio I do not use any AppImages at all.
All that being said, my suggestion would be to focus on Debian (and Ubuntu) as the distribution of choice for the professional audio platform in Linux. It’s easy enough to build something for Debian that will work and be stable and if there is a library or dependency issue to use the Ubuntu library/dependency for Ubuntu and its derivatives.