I don't think its fair to call it a ponzi scheme, if it were a ponzi scheme then the founder of Bitcoin would have sold some coins... and he hasn't. If he is even still alive, and isn't actually the CIA.
There are actual crypto ponzi schemes (or MLM schemes as they are better known today) being closed left right and centre.
I don't know WTF bitcoin is, but its never going to work as a currency or replace cash.
Anybody who thinks bitcoin or any other crypto will replace cash will first need to explain how they intend to mitigate the following:
1). The 15% of people in the world who don't have access to electricity
2). The 50% of people in the world who don't have access to the internet
3). The 37% of people in the world with no access to a mobile phone or a mobile network.
Consider the three factors above, and then tell me how a crypto could ever replace fiat money as a major global reserve currency. It can't, as simple as that, no matter how cheap and fast transaction fees can become.
Blockchain technology definitely has a roll to play in 'the city' for trading platforms etc, to effectively serve as a promise note or IOU, but not in the real world....