That's an interesting hypothesis. Only one problem: it's obviously false and falls apart at the smallest amount of scrutiny. MM Hunter parses on M-Odyn outnumber SPriest parses. Hunters are the 2nd most taken spec for M-Odyn period according to Warcraft Logs.
SPriests only outnumber Hunter on M-Guarm by 27 parses. That means their representation is a mere 4.5% greater than MM Hunter... which is still the 4th most taken class to M-Guarm. If you include BM, then the Hunter class is brought significantly more than SPriest.
Oh and for the public parses on M-Helya, MM Hunters outnumber SPriests by 28%. The bottom line is MM Hunters aren't being sat. Period. Not for SPriests, not for anyone. They are, in fact, being stacked. Repeatedly, on every fight, on every difficulty. You don't get there by being a "mediocre" class.