What if all the rich people come together and buy most of the BITCOINS can this lead to the control of power again in the hands of few.
If they do have the money to buy on,why not? They can manipulate price on that one and could affect the price easily but not totally the owner of bitcoin.No one owns bitcoin but as an investor you would able to give effects but thinking off to be a Big investor on bitcoin you would need billions of money in order to be considered as a whale for sure 
to be honest, a small group of actual elites could completely corner the market on bitcoin. this has hapened before, in traditional insdustry with way more mundane things. look up the sumotumo copper affair, and follow the related Wikipedia links. Its a pretty interesting dive.
the less considered vector of attack by a whale group, however, is if they have the common sense to invest heavily in mining. for making a better miner, then funding the production of said miners, they could corner the mining market specifically, and dominate the network with superior hashing power. this would cost so much less to do than manipulating bitcoin price; why waste money changing the price when you can simply control production?