I don't think bitcoin is a ponzi scheme. First of all, bitcoin is decentralized and this is the strongest argument in favor of the fact that it is not a ponzi. Bitcoin has very good growth prospects, you just need patience.
For the layman, let alone those easily influenced by the issue, would surely assume bitcoin is a ponzi or bubble scheme. The most relevant reason is that of the very high price spike.
While you assume that bitcoin is not ponzi, it means you understand exactly what it is cryptocurrency.