Yes, this can be manipulated, but for what? Whales get a steady profit from Bitcoin volatility and I am 99% sure that none of the whales will destroy the market. It is not profitable, it will bring loss, therefore it will not happen
If they are in group of whales and making an organized sell or buy order to manipulate they could take advantage of the whole market. You see there are many panic traders aswell who aren't really experienced in trading and rather making trade orders simply based on fear. I'm sure the whale are trying to target those kind of people because that's the easiest.
Whales live off small panic traders. Two years ago, we saw how whales can hit a jackpot when Bitcoin grew to 20k and collapsed at once in a flash. Its just needed to be careful and trade with a cold mind.