I don’t know I buy that about D&D at all actually.  Appendix N exists for a reason.  And that reason is “Read this stuff to understand all the tropes that you’ll want to bring to play this game successfully”.

I mean Gary and Dave clearly had ideas of what they were creating at the table and I’m sure it was more than a little “Take some Paul Anderson add a dash of Andre Norton, and mix in some Moorcock.”  I mean the alignments, the Vancian magic…elves and dwarves, oh my; it was a grab bag to be sure, but it was a grab bag of all that 60s and 70s era wierd fantasy along with a bunch of that older pulp stuff.

It was rather all over the place and eclectic, and hadn’t yet been labeled and squeezed into a genre for the benefit of big chain book stores, but there was still a base line of common elements that informed that early play and thus served as the common “Cultural Literacy” that the early players shared.