Does Proof of Stake Lead to a Positive Feedback Loop?
Even if the dynamics are interpreted in the most basic way, it does not lead to this positive feedback, rather it maintains the status quo. If there are miners with stake of 40%, 30% and 30%, they will get 40%, 30% and 30% of the rewards respectively, so the ratios will remain at 40%, 30%, 30%.

For example, if they start with 40, 30, 30 BTC, and 10 new coins are generated, they will be distributed 4, 3, 3, so the new wealth will be 44, 33, 33, which is still a ratio of 40%, 30%, 30%.