Ugly paintings are a ponzi scheme. Jordans are a ponzi scheme. My wristwatch collection all of which I cant wear at once is a ponzi scheme. A 30Y foreign bond you dont hold to maturity couponing a currency you dont spend is a ponzi scheme. The publicly listed stock you bought on the secondary market with no dividend and that you dont vote in is a ponzi scheme.
This is just a boring semantics-based critique by the lazy.
Yes, the market value of a thing is, by definition, based on the consensus of those in the market. The market for bitcoin is broader and broader as it gets more institutional support and distribution. And lots of those things dont need real world utility.
My gold Philharmonics I never intend to smelt into jewelry or onto a circuit board and nobody will ever buy it for that purpose either. I like the idea of having it. I know its supply is finite. I know its value is speculated with some vague correlation to financial markets. I know other people would like to have it. Its my ponzi.