True Left

"2) The teachings are real, but they were just grifters who themselves didn't believe what they taught. (Then why not teach something easier to follow?)"

Exactly! If he was simply trying to lead people astray, and was bashing Brahmanism out of envious spite, wouldn't it have been easier for him to just teach his followers to accept the beef-eating, cow-sacrificing, Vedics as the rightful rulers? What reason would he have to oppose them? He was a Kshatriya after all, so he would have had high status in the hierarchy. And his followers could have still retained their non-Aryan habits and be accepted among them.