The market cap is very easily manipulated because it doesn't relate to the actual liquidity of an exchange. People on an exchange can often change the market cap of a coin with just a few Bitcoin, sometimes even less, and the price changes very dramatically. Even Bitcoin exchanges have insanely low liquidity right now.
Bitcoin exchanges have always had a very poor level of liquidity. In order for a whale to cash out a few thousand coins, depending on the exchange, he is likely able to push the price 10-20% downwards in one single dump. And then I am not even talking about the effect of stop loss orders that might get triggered, which will result in the price to tank even further. So yes, it takes little (in relative terms) to get the price to tank heavily.
Yes there are whales but till date today I haven't seen a single person or a group of people manipulating the price of bitcoins. See the cap is too big for a group of people to cover, yeah if some big companies/industries collaborate and make the market swing I can understand but that wont effect the market by much too.
I would agree when the price for bitcoins was 100$ but now it is $1000+ mate and you know how difficult it is to manipulate a btc market alone.
I think you didn't understand anything of my post, plus you lack the understanding of how the Bitcoin market and everything around it works.