Those billionaires aren't dumb, if they were - you wouldn't be writing this post. It's the followers that are dumb, I'm afraid. That's the only threat there is associated with these attempted manipulations. Not the whales, no someone powerful selling crypto (it only has a temporary effect), but the people, that follow the lead. And that's the main purpose.
If you follow the news it can be seen that the most significant changes in price are driven more often by the info on the media, someone's talks, rather than the actual purchases.