The parts are fragmented. Procedure concepts and designs need to be
melded with aircraft performance and ATC procedures.

Yes! There might well be a market for such training. An online
training course might find a larger market, though. But it would have
to be tough and thorough, not a "fluff" course.

The fact that all this is fragmented is something in particular that
an instrument pilot needs to hear. It would explain a lot of
inconsistencies.