> For me the dist file is something ready to deploy / use whereas the makefile is for developers.

we don't provide source tarballs with half of the files. that's news to me. README, tests files, everything is always added in thetre

> That's also the reason why we have optional dev-deps and required deps.

You are mixing two things: definitions of dependencies and test dependencies vs runtime dependencies

We provide a definition of what is needed in the tarball to run the tests.