>> consensus will be set by the few whales, who will maximize their rent extraction at the expense of numerous small players
Aren't you just describing capitalism here? The people that created the system and own the biggest share of it have gigantic influence on it. Matter of fact, isn't that exactly what happened in ethereums PoW network, too? The developers decided to switch to PoS regardless of what the current participants want.
In general, isn't the idea of using PoS that if you aren't happy with the current system, you can easily fork into a competitor? If enough people think the current system is unjust, then you can switch to the new one, where you will be part of the development. At the beginning of the fork you also wouldn't need that much compute, as PoS is more efficient and you aren't going to have many users/transactions in the first place.
Since it's easy to switch currency (at least easier than privately setting up a Dollar 2.0), members of the original currency have to behave fairly, else people are going to switch. Note: The thing people are switching to doesn't even have to be better in any way than the original currency. It just has to have different controllers to influence the members of the original system.
The way I see it, is that there's no meaningful way in which PoS based currencies are worse than the current monetary system: large stakeholders in current global currencies also have gigantic leverage (think of money printing during the pandemic or bailouts after the 2008 financial crisis). The real advantage I see with PoS systems is not the system itself, but the tooling that comes with it and allows for the development of competitor currencies that check the power of each other. With current global currencies there's no checks-and-balances system inside the monetary decision making process, while a fleet of independent PoS has the chance for checks and balances to be induced through competitive pressure.