Not really. Whoever created these distros had a specific vision they wanted to achieve. Debian is one thing, Arch is another. The world is richer for having both.
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.
90% of distros' "visions" is ultimately just providing a general-purpose desktop/laptop OS. There's indeed an insane amount of wasted effort, both on developers' part but also users (skill portability is an issue because no 2 Linux distros/machines are alike).
I would argue that those are either similar enough to not be wasteful or dissimilar enough to not be redundant. Lubuntu is just Ubuntu with some minor differences in default packages and configs; there's not enough difference there to be wasteful. OTOH, Ubuntu, at least for a long time, was genuinely much more friendly to beginners than Debian, partially just because they could get patches in faster, and partially because they had a looser standard around non-free packages. There was divergence but for a good reason, and the projects have largely collaborated over the years so that the source code changes are shared where sensible but they target slightly different audiences with different support systems. Well, there's also Canonical just being Canonical but there's no way to solve that.
