Debian and Arch are different enough that the argument isn't about them. The issue is the 100's of distros that could be replaced with just "install <major distro> and do apt install X" (or some other trivial thing like changing the default to KDE instead of Gnome).
You can also replace that with "just install Windows", or "just use macOS".
Hell, you use this for anything; "why make a new album, movie, or book when there are already thousands upon thousands of them? Yours probably isn't any better!"
You completely misunderstand. Windows and Mac are different enough from every linux distro that the argument isn't about them.
And if you're going to start talking about copy-rightable works of entertainment, then yes if you write a book based off another book just with 1 extra character (analogous to "install <major distro> and do apt install X") then that book would violate copyright and should not be written. It's the lack of copyright in FOSS that allows all the pointless duplication of effort with all the almost identical linux distros.
