No, I went into a bit more detail in the next sentence. If we were to assume a billionaire with nigh-infinite wealth he would probably still have quite a challenge ahead of him if he wanted to manipulate the Ethereum blockchain.
For starters you can't simply go up to the existing stakers, hand them a big stack of cash, and tell them "your Ether is mine now." The Ether that is staked is not for sale. It can be put up for sale, if the staker desires, but given that it's currently staked and not on an exchange somewhere that means that the stakers don't currently want to sell it.
So Mr. Moneybags is going to have to buy Ether from external exchanges and put that up as a stake such that they will have 2/3 of the stake while accounting for the fact that he doesn't own the 20 million Ether that's already staked. So he's going to need about 40 million Ether (40/(40+20) = 2/3). At current market prices, 40 million Ether will cost $75.5 billion.
But there's yet another hurdle. There isn't actually 40 million Ether for sale on the exchanges right now, either. There's only 120 million Ether in existence, and much of that is bound up in various contracts (staking, stabletokens, layer-2 rollups, etc). So if he goes to the exchanges and just starts buying whatever is available the market is going to see that there's an insatiable demand for Ether. The price of Ether will rise. If it rises enough people will start prying their Ether out of wherever they've stashed it, because now they can cash in and make bank off of Mr. Moneybags who's making it rain over on the exchanges. It's going to cost way more than a mere $75 billion dollars. Elon Musk is currently worth $238 billion, I wouldn't be surprised if his entire net worth wouldn't be enough to accomplish this.
Let's say that Elon and Bezos and a bunch of others pool their money to do this. This is economic activity without historical precedent, a vast transfer of wealth from the pockets of the rich and powerful to... a whole bunch of random cryptocurrency holders around the planet. This will be very notable, I'm sure, and I suspect that there'll be major governments very curious about where all this money is going and why. They'll want their cut, or they'll reflexively go "don't understand this so better ban it", or assume it's a big money laundering thing, or something. Yet more obstacles to overcome. It's possible to overcome them but not easy on this scale.
continued next comment, for the first time I've exceeded the comment size limit