An interesting theory to say the least...
But the major flaw I find in it personally is that in Harry Potter the "Witches" (which if memory serves is a word that is not used in the books) aren't so much a "secret 'overclass'" - as they don't run or control the world of 'muggles' (non-wizards) - but are rather 'seperatists'... seeking anonymity as a means of preserving their 'culture' and way of life...
...and after all... it is a fantasy... one could draw all sorts of analogies from almost any source...
The problem is proving that there was either 'intent' in it's writing or that it is being used as a 'manifesto' or 'prototype' (as with the example of Oberon Zell's book mentioned above)... without that it remains just another 'conspiracy theory'...
However... you're equally entitled to your views as anyone else here so long as they abide by the forum rules...