Well yeah, it's not exactly a Ponzi scheme per se, but it is a lot like oil and other natural resources, but they're a resource and not a currency. It is quite a lot like a natural occurring Ponzi scheme though. I don't anyone has actually explained this yet, the core point I'm getting at is if the supply is inherently built to continually diminish, then wouldn't the price continually increase, and that in itself is can't sustain a stable currency and the people who invested early will never be at risk because their asset will be guaranteed to continually appreciate in value
The same could be said about land. If I bought several hundred acres of land in rural PA as an investment would you say that I am investing in a naturally occurring Ponzi? After all the supply of land is limited.