No. A Ponzi scheme is paying existing investors with the deposits from new investors. That's not what's happening here.
Once new investors dry out and price collapses stakers will be rewarded with same amount of coins now worth nothing (just like IOU in Ponzi) and will be left with staked coins of 0 value, just like in Ponzi.
One could design a "staking" system that is directly reliant on other people's money coming in for your payout to happen. This is not what is happening here.
Staking as done by this protocols itself never promised you anything but a yield in the crypto currency itself.
Maybe you think crypto in general is a ponzi scheme because people only want to sell to new entrants for a profit, but that's a different issue (not not necessarily true - it also works with a fixed set of people you keep wanting to gamble).
That's a fixed percentage promise. There's relly no difference if it's expressed in crypto coins or in entries in the database of a software system of ponzi schemer.
If you have a fledgeling crypto on its ride up, it's not only fueled by new investors but sustained by new investors. If the coins are minted at will the supply will eventually exceed the demand and the coin will start loosing its value. And then the inevitable crash to the bottom happens. It's crypto equivalent of hyperinflation of normal currencies that happens when money supply exceeds demand for money associated with economic development.
> Maybe you think crypto in general is a ponzi scheme
I don't. I just feel like promising fixed, large percentage gains makes something Ponzi scheme. Something like Bitcoin or Ethereum that have tight control on coin supply are not ponzi schemes. Those are just new type of commodity. Mildly useful, but scarce, unique and easily transferrable and divisible.