So actually people who have more of the coin will get more rewards by more mining. So for example if you owned 1% of all coin mined, you'd get 1% PoS blocks. Does that mean that someone with 0.00001% will never get PoS blocks and therefore never gain anything from mining it? If so, most people will bail out reducing it's price and finally killing the coin...
it's like mining if you put 0.00001% of the hashrate you will get almost nothing, there is no difference on how they work
usually it's more easy to dump pos because there is no electricity there, so no reason to hold, nothing is backing it up like with pow