Remember, this whole thing about crypto is largely decentralized, thus, there is no single authoritative body in control of the crypto market. Although there are few centralized platforms among crypto, the market is largely influenced by the efforts and influence of the users of crypto. How well sellers and buyers treat the coins on the market affect the performance of the market.
Generally speaking, there are no specific people who are controlling the market, just like what you have said, this market that we have is decentralized. But if you came up with your idea because you noticed that there are big changes that is happening in the market every single time, it is because of the whales. Whales are the people who have the biggest amount of cryptocurrencies, meaning, if they dump their altcoins whenever they like, the price of that altcoins in the market would change also, it would affect it, but it doesn't mean that they are controlling the market.
It is just a strategic way for them to gain more profits if everyone will dump their coins also because of panicking, being afraid that it might drop even more that is why they might do panic selling.