You are right the whales are the biggest gainers as the power to control the network have been handed over to the ethereum holder who stakes the balance of the pool to process transaction, there is one strong limitation to the proof of stake consensus which is the ability of the highest ethereum holders to control the process of transaction processing in the network. There is a fact that proof of stake will less the energy consumption by the ethereum holders and aside from this I don't see much advantage the merge has over proof of work and if we must view it closely the proof of stake favors the big bag holder who can afford to lock their funds in the staking pool for a long time and giving them the power to control the network.
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Since when the whales are not in control over anything in this world?
It is a common fact, not just in crypto but in real life they are the ones who is manipulating the flow of the market, politics, etc.
PoW consumes a lot of resources, we might not see it from our perspective but it is real and unsustainable in the long run. PoS is healthier compared to PoW in this case, so we can not conclude anything yet at least for now. There is pro and con, but I believe it is an upgrade instead of a downgrade.
They won't postpone it for years if they do not have a proper reason to do it.