Cosmic looks very interesting and very unfinished. Maybe it is the teal accent, maybe it is janky transitions. Nonetheless, I’m happy to see some fresh Linux Desktop Environment.
As a native English Speaker, "scratch-built" is definitely not a common term (I was confused when I read this).
In this case, its an extension of the phrase but using the word built instead of made.
Ref: https://grammarphobia.com/blog/2017/02/scratch-made.html
My father used to talk about 'Scratch-building' his WWII dioramas and model vehicles/tanks. While you could use a phrase like 'Scratch-cooked' rather than cooking from scratch, I've never heard but someone would not think the former meant something different to the latter.
That kind of defeats the purpose of the distro (or a big part of it at least).
Giving any choices defeats the purpose of a distro?