>> Do the Linux distros use pip to build their packages?
>
> Not that I am aware of.

Fedora's build macros for Python projects currently rely on running
setup.py directly, but we've been considering switching to pip instead
since 2013 or so. PEP 517 is likely to provide the impetus to switch
from "maybe we should do that" to "we need to do that, at least if
setup.py is missing, and potentially always, so we get more consistent
installation metadata"