could be, when you have a number that many or more than 50% then all the things you can do include control bitcoin. I'm sure, that there are currently doing so.
there are millions of bitcoin spread, if you have at least 100k bitcoin. I'm sure you can manipulate the price of bitcoin. even able to control a market of bitcoin.
The key is to have a very large bankroll
You still can't manipulate the bitcoin price even you are the most riches man who hold tones of bitcoin you will not waste bitcoin just to manipulate it, maybe the volume of trading in exchange can be fake but not the bitcoin price many people will be react on this.