>Your theoretical Debian distro might be fine for general purpose use, but there may be people who want a distro for games, or a wide range of hardware compatibility.
So your installer installs a custom compiled and signed kernel, proton packages, and whatever else needed for gaming on the base install? Just like every full distro does for updates... You know you can have multiple kernels and have them be selectable - with one default selected through grub-setup - at boot time, yes?
>and a distro bundled with certain desktop GUIs and applications.
That's what package managers are for. You don't NEED to install some super special distro just to install "supercleandestop" which is a meta package that just install all the crap it needs to run, including the actual packages that install the desktop. You could even have it set up as a task in Debian based systems so users can install it with tasksel. I don't know WHY you would want to do that, as just installing the metapackage is 10,000X easier, but you could. Especially since versioning is ( fairly ) clean in Linux, and you can have multiple versions of the same library installed if needed.
>there is no one way that would make everyone happy - no matter what changes you add on top of it.
As a matter of fact, especially for 99% of the people making the specialized desktop / workstation / specialized for X distros, having a standard base to install on to would cut down on their work SIGNIFICANTLY, allowing them to work more on the special bits they want to have people use. No more need to repeat work over and over again compiling and making ISO's that are 99% identical to every other ISO out there. Just make sure your package is compatible the the ONE base version, and it can go into basically any repository and be used. As an added bonus, they wouldn't have to compile different versions for different distros that have differing package names / version numbers either. Anyone could build a SINGLE PACKAGE that will run on a specific version number of the base.
That's what Snap / Flatpack / Appimage are trying to do for devs, but it comes with extra costs compared to bare metal running your program.