So, apart from the guys shouting "rich will get richer"
It's not that. It's the rich will have untouchable anonymous power. There is no way to stop a cabal of people from taking permanent control and reversing transactions discretely.
But with PoS they need 51% of the entire wealth of the currency, to do so, and at that point why would they do it? they will only undermine themselves when discovered because the value of the currency will plummet.
They would never allow themselves to be discovered. There is no method of tracing controlling shares to individuals. Everything would be done in secrecy using TOR or other darknets and disinformation campaigns would be waged.
With PoW, they only need about 10% of the wealth to overwhelm the mining hashrate, because the current Bitcoin mining operations are worth about 10% of the Bitcoin marketcap.
There are many countermeasures against PoW attacks precisely because the hashrates are known. There are still vulnerabilities with Bitcoin, but because the transactions are more transparent, there will be better engineering solutions.