[EdHominem]

Well, we've been making validated structures where a checksum (essentially a pre-cryptographic hash) of the last data-block is included in the next since the sixties. (And I suspect much further back in an accounting context.)

The difference these days is a protection, via proof-of-work, against just creating a new, valid, chain by editing the old one.

That proof of work, to be translatable into a dollar value, requires a market for the proofs and that's the currency part. (Without that you don't know the true market value of the energy required for the PoW.)