No, that's not correct. In traditional PoS, your expected value of staking is directly proportional to your staking amount. The effect of compounding sounds like an issue -- but what you find is that with a probabilistic system the smaller stakers still, on average, approach the same rate of compounding as well.
So long as a large staker and small staker are always staking, their rewards are proportional. There's a bit of statistics involved if you want to prove it, but it is true.