The "ponzi scheme" is named after some italian guy that ran a business that used new investors' money to pay old investors, making it seem like their investments were bearing fruit. Now, that probably doesn't sound like cryptocurrency to you yet, but I hope to make a compelling case by the time you finish reading this page.
Have you ever noticed when someone invests in crypto, and it immediately usurps them and becomes their lifestyle? This doesn't happen to everyone, but I've seen it occur at a roughly 50% split. This happens because their investment holds no inherent value. They simply purchased some immutable bits: they don't mean anything, they don't do anything, but that's where the value comes from: they cannot be changed. This is why the crypto-kings are so preoccupied with upholding the legitimacy of their bits. They need new investors to uphold the value of their holdings, or it will implode.
The blockchain is neither immutable nor decentralized.
The blockchain is not decentralized. Although you could run your own node - and waste hundreds of gigabytes of your precious storage, not to mention bandwidth and processing power. Nobody wants to do this; this has caused several third parties to show up and provide APIs for interacting with this blockchain. If any of these APIs see cause for blocking (or - god forbid - alter) your queries, you'll have to move to a different provider, not dissimilar to existing online payment systems.
The blockchain is not immutable. If someone were, for example, to commit child abuse content to a blockchain, or if there has been a major hack (this happened), the corporation managing said chain can simply roll back to a previous version of the chain and start again from there. Although neither of the blockchains prohibit the existence of the other, the value of the "currency" in the pre-fork chain will plummet to zero, either because the robbed people want their tokens back, or because nobody wants to host child abuse content on their node.