There's always a comment in any HN blockchain thread where the commenter disproves the need for a blockchain by proposing just to use a blockchain instead.
Your protocol has to use a consensus mechanism if you want to reliably make progress, and be able to recover if you make mistakes, this is exactly what a blockchain solves
That you _can_ solve it with a blockchain doesn't mean that you can _only_ solve it with a blockchain.
M valid signatures of N authorities is a consensus mechanism that just needs public keys. You don't need a blockchain if you're prepared to trust a set of authorities like stripe and their trusted partners.
