But it's still a Ponzi scheme in that you're paid out in the thing you stake, so you don't necessarily have any more value with respect to an external reference.
For all practical purposes, you could exchange the currency for something else. But that's outside the scope of the staking system as defined.
I'm not making any negative or positive judgement on the system, Ponzi scheme is just a description of how it operates. Similarly, any stocks that does not pay out dividend is also a Ponzi scheme.
That’s not what a ponzi scheme is though. The most important thing about what makes a ponzi scheme a scheme is that the person running the scheme is obfuscating where the money being paid out comes from. It’s when someone pretends they’re doing something highly profitable to attract investors, but actually when they pay people with what they claim is profits they’re actually just using the money from other investors. The defining feature of a ponzi scheme is not that if no one would be willing to buy if off you, if would have no value (that’s definitionally true of all objects). It’s that if new people stopped investing in the company, the company would fall apart. There is no value in a ponzi scheme separate from more money piling into it.
This is very different from a stock that doesn’t pay a dividend. While you’d never get money out of it if no one was willing to buy it, what stocks generally promise is some amount of ownership and voting rights in a company (which theoretically could result in dividends, if enough stock holders agreed). That said ownership ended up not being valued by other people does not make it fraud. You can certainly feel free to believe that stocks that don’t give dividends are worthless though, that’s a separate question really.
I generally come down on the side that the major cryptocurrencies aren’t ponzi schemes, or fraud in general. (Plenty of fraud in the shitcoins, of course). Ultimately you decided to buy a data point on a ledger in a distributed system, and that’s what you get. But…well, mining sometimes confuses that. Without enough people coming into the system to buy new coins, the miners would start shutting down until none were left. Much like a ponzi scheme, crypto currencies seem reliant on new blood to keep functioning to me. Don’t know if that makes them a scheme necessarily, but they’re more adjacent to it.
The definitions you use match the recent failing crypto exchanges behavior. They completely obfuscated what they were doing. They had made loans if hard crypto assets to other companies, other exchanges, and either refused to describe the situation or outright lied about it.
For all practical purposes, you could exchange the currency for something else. But that's outside the scope of the staking system as defined.
I'm not making any negative or positive judgement on the system, Ponzi scheme is just a description of how it operates. Similarly, any stocks that does not pay out dividend is also a Ponzi scheme.