Note that at least splituser is being used outside the stdlib: packaging
(which was intended to be part of the stdlib) used it, and hence so do
distutils2 and distlib (by sharing parts of their codebases). Of course these last two are outside the stdlib.

Similar functions are reimplemented outside the stdlib (e.g. see parse_credentials in pip.download).

If the only reason for not exposing these is documentation clutter, surely there are approaches to minimise this. If the reason is that future implementations may change or remove them, that should be clarified. But since the basics of an url are unlikely to change, I don't see why these functions might be removed in the future.