>ultimately not a ponzi scheme
A ponzi scheme has a specific definition. By your modified definition certain commodities, such a gold and oil, are ponzi schemes because they become scarcer as time goes on.
>it doesn't take much to crash the value of the asset.
Looking over the past few days, the price is 8% or so below what it was. Not much of a crash. Predictably, as the market for Bitcoin has grown it has become less volatile.