Are cryptocurrencies a pyramid?

No.

Cryptocurrencies are not a financial pyramid as for her holders any payments are not provided. Also, nobody guarantees growth of the price.
The financial pyramid (Ponzi’s diagram) formally guarantees payments and profit to all participants. And some time (depends on the success of the project) fulfills these obligations for early “investors” due to the attraction of financial resources from newly arrived participants. The influx of new users comes to an end — payments come to an end. Came right at the beginning — you in plus. Appeared in the bottom of a pyramid — were left with nothing. Execution of obligations to all participants is certainly impossible. In it all sense of financial pyramids.

In case of cryptocurrencies you just buy them at the price which was read acceptable. Are ready to pay $18000 for bitcoin? Please. We will assume, the transaction took place. After that nobody, nothing shall you. You — the owner of bitcoin. Nobody guarantees you its share repurchase. Yes, you just spend money for a digital asset. And if its price falls up to $10, then all of you will possess still bitcoin.

The similarity with pyramids can be marked only that the price of cryptocurrencies grows including at the expense of new participants. But it is just laws of the market. Then demand, that high price is more.