For every futures short there is a futures long on the other side of the contract. If you were to attempt to suppress the price of spot bitcoin with futures you could buy enormous amounts of short futures contracts. This would cause the futures price to be well below the spot price, ie, futures would run a discount. Then market makers would buy futures and sell spot bitcoin to capture the risk-free spread.

Odd then, that CME, the largest bitcoin futures market, has been running a massive premium for well over a year now.

This is evidence that the futures markets are driving spot prices up.