Do you mean regulated futures, because they were launched when the market topped? That seems unlikely since they're cash-settled. They can short all they want on the CME market but that doesn't equate to bitcoins being dumped on exchanges. Unlike an open-ended ETF or physically settled contracts, there's no mechanism for cash-settled markets to lead the spot market.
I'll bet most of the spot market action in recent times was purely to provoke action on Bitmex. I can't be arsed to do the sums, but it might well pay to screw with the real market to profit on these cash settled markets. There aren't many people left to put up much of a fight if you make a strong move.
It seems farfetched to me that large CME accounts would expose themselves to so much counterparty risk at various dodgy spot exchanges just to short the CME more effectively. That's something bitcoiners do on wild west exchanges (including Bitmex), but probably not serious institutional traders. Last I checked, the regulated markets didn't have very high volume to justify that either.
I'm less talking about manipulation in general anyway, and more to the idea that "CME futures launching = Wall Street shorting Bitcoin to the ground." If anything, Bakkt -- especially if it ends up allowing leverage -- would be a much more effective vehicle for that. Between leverage and conventional Wall Street accounting practices, Bakkt could dilute supply and the spot market will follow, if it has high enough volume.
