No matter which algorithm, in order to determine which blockchain is the correct blockchain, Proof of Stake blockchain users need to trust that they have been told the correct initial account balances. How can you prove in a decentralized manner whether you are mining the correct blockchain? You can't without outside help. This makes Proof of Stake practically useless.
And along the same lines, POW-POS hybrids are only as strong/decentralized as their Proof of Work component.
Agreed?
The point here is that if staking is done by a lot of people than it won't be centralized, as long as there are a lot of wallets with a lot of stakes than the issue is nothing and not to be worried. However if people start to buy a lot and whales get as much as they can than there will be a little amount of people who end up with most of the money and than they can do what you are basically saying.
Hence, all of this depends on how many people will be staking and how much the wealth will be distributed, if its at the hands of few rich people, you are right with your worrying but if its distributed equally than there is no problem. Obviously, human nature is greedy and this could end up being a problem later on but at the same time if someone wants to buy a lot of eth to do this than you will sell your eth for a lot higher in the future which allows us to get out with profits at least.