> They are also able to do it optimistically, refunding people and then adjusting policies if it turns out the policies are being abused. This stuff is very hard to encode into a decentralized protocol.

Whats the nexus between centralization and ability to refund? Regardless of centralization i can cancel my credit card to stop you from clawing back an optimistic refund, regardless of centralization the protocol could force a waiting period before withdrawing optimistically refunded monies, etc.