Moreover, anyone who can stake their tokens to produce blocks will never sell you enough tokens that you'll be able to compete with them for future block rewards. Put another way, the value of a staker's token-minting stake is at least equal to the expected ROI over its lifetime (much like how the value of a stock is worth its expected dividends over time). PoS is a digital manifestation of a hereditary aristocracy -- you can almost never buy your way in; you have to be a first mover.