It is plausible, but begs the question. If these whales are dumping 100s of BTCs at a time, they would have to run out, or buy back at some time. Do you suspect they are manipulating in both directions? I suspect the longer the adoption rate of Bitcoin remains below a critical threshold, the longer we will be exposed to the demons and phantoms.
Never forget the fact that people who started mining well before 2012 must be having a huge amount of coins and they could manipulate the price of bitcoin,since it is a highly volatile coin everyone gets a chance to get back even if they sell off at a higher price.