[WJW]

There's an interesting academic paper that I can't find anymore where the authors analyze the game theoretic edges of PoS systems. Basically: since the thing you need to mine is the same thing that gets mined the optimal strategy for anyone holding a majority of a PoS coin is to never spend more than half of your mining reward so that even someone who manages to buy all the coins that become available on the market can never catch up to you.

Of course, this does omit some real-life considerations like people needing money for other reasons (to pay taxes, when they die, to buy a house, etc) but the basic principle stands: any initial whale in a PoS coin will basically never be dislodged if they play the optimal strategy.