I don't think you miss anything.

POSIX compliance is a headache which is not only hard to get right but also strongly limits your interfaces and internal tooling.

Many scripts still will run with non full compliance, but that doesn't help if you try to build for OpenBSD.

Also I'm not sure how they ended up with 400 deps for coreutils. I would have expected much less. But yes this means at least until better code signing and so on is the default this isn't at all appropriate for the base of any OS.

I just which the author would have written it a bit less mean in it's wording. (Probably was just annoyed, but sill).