Depends on the PoS design. Some have a limited number of stakers, or give stakers voting rights in an on-chain governance system. Neither is true of Ethereum's proof-of-stake, but it's not quite in full production yet.
As for the rich getting richer, that's no different from mining. Stakers have much lower ongoing costs, but the rewards are lower too so their percentage annual return isn't necessarily better. And everyone gets the same return so there's no economy of scale, which is not true of mining (or, for that matter, savings accounts).
As for the rich getting richer, that's no different from mining. Stakers have much lower ongoing costs, but the rewards are lower too so their percentage annual return isn't necessarily better. And everyone gets the same return so there's no economy of scale, which is not true of mining (or, for that matter, savings accounts).