Bitcoin is completely decentralized, one or more individuals, institutions, and groups do not control Bitcoin. Bitcoin whales are organizations, individuals, and groups that hold 1000 or 1000+ bitcoins. Yes it may be somewhat true that bitcoin whales may temporarily have some effect on the bitcoin market. For example, if Michael Sheller sells all his bitcoins in the market at once, the bitcoin market will be affected to some extent. Bitcoin whales will not completely destroy the Bitcoin market.
Control can be not only direct, but indirect only: you don't need to affect a market with one big sale or buy, you need to provoke a wave of deals in a way you are interested in. So you can make multiple small deals, use media and viral marketing and other tools you can to achieve your main goal: to get profit from a trend you are interested at the moment. Yes, it is not so easy, but who would like to play on a market where one player can directly control everything? No one, so that only player will not get profit as well.