PoW is leader based consensus. It’s slow and can’t handle millions of simultaneous payments. Why do new distributed ledger technologies still prefer to use it, when there are other, far faster consensus algorithms out there?
More seriously, if the name of the game is efficiency then a distributed ledger isn't the answer.
And if you're only looking for immutability, then time-stamping is already good enough (and available since the late 90s or so). I suppose you can use a Merkle tree and then proceed to put "Blockchain" in your marketing materials without technically lying.
600MB every 10 minutes is no sweat for even modest internet connections nowadays.
With technology like weak blocks and the lighting network and other side-chains the network can handle it no problem.
That's all pretty moot at the moment as BCH is averaging ~50kb blocks.