If you want to call this a Ponzi scheme, then you have to be fair and consistent and call the dollar system "the other Ponzi" scheme too (because your 1 dollar purchasing power is not the same as todays).
Which one would you rather owe you?
There's a massive difference between "we issue a token which has purchasing power because people are legally required to obtain it to pay their debts and taxes. Its purchasing power is allowed to slowly diminish over time, but it will continue to be demanded because people need it to meet obligations" and "we issue a token and lie that it's worth a dollar because it's backed by an equivalent quantity of dollars. Its purchasing power will collapse at the time we stop redeeming them for dollars, whether that's because we run out, get arrested or move on to the next grift with lots of un-redeemed dollars in our pockets"