Goldman Sachs take on cryptos - very good article that explains cryptos using terms that I can understand (without much crypto jargon).

https://www.zerohedge.com/markets/amazon-information-goldman-initiaties-crypto-sees-ethereum-overtaking-bitcoin 

The term “cryptocurrencies”—which most people take to mean that crypto assets act as a digital medium of exchange, like fiat currency—is fundamentally misleading when it comes to assessing the value of these assets. Indeed, the blockchain that underlies bitcoin was not designed to replace a fiat currency—it is a trusted peer-to-peer payments network. As a cryptographic algorithm generates the proof that the payment was correctly executed, no third party is needed to verify the transaction. The blockchain and its native coin were therefore designed to replace the banking system and others like insurance that require a trusted intermediary today, not the Dollar. In that sense, the blockchain is differentiated from other “digital” transactional mechanisms such as PayPal, which is dependent upon the banking system to prevent fraud like double-spending.

So cryptos are not 'currencies', they are to replace the banking system...