Market cap is the measuring stick of fools, especially in this context.
There's no way that $280,000,000,000 of Bitcoin could be sold, so it's irrelevant that the market cap is supposedly that much. It also doesn't mean that that much was invested in it.
The futures don’t directly affect the price of BTC but the hype brings exposure.
They could affect the price very much due to the sorts of people that are interested in these more legitimised investment systems, and the ability for richer groups to use larger amounts of money.