The Linux base system is managed by the package manager, leaving local for the sysadmin to `make install` into
There is no such thing as a Linux base system.
Separate components, separate people.
Hence the term Ganoo plus Leenox...
Every occasion I’ve seen GNU coreutils installed on BSD, it’s been outside of the base and thus installed outside of /bin. Eg /usr/local or /opt/homebrew
In most distributions yes, there is Linux and then there is userspace on top of it. What you call "base system" is actually part of userspace, which has nothing to do with Linux itself.