IMBW, but I think I recall the Python packaging guidelines specifically
said that you could or should (I forget which) just BR python-devel and
not BR python-setuptools at some point. At this point there seems to be
no explicit mention, but the sample spec file looks a lot like a
project that uses setuptools, but does not explicitly BuildRequire
Packages building for Python 3 will need
And also this:
Packages MAY use the automatic Python dependency generator. This generator uses upstream egg/dist metadata (such as setuptool’s install_requires)
Considering the file vs dir difference in metadata storage, I would say it's fair to expect dependencies to be strict.
I myself don't have any Python packages yet, but I'll try to pay extra attention to python3-setuptools in the future :).