> Could you then say that this blockchain really provides nothing that a traditional centralized system wouldn't?

Blockchains (in general) enforce not only open code, but open data.

Technically, nothing prevents traditional banks to offer standardized easy-to-use and easy-to-onboard API access to their financial data, but in reality incentives are not there (quite the opposite).

Blockchains are a contrived way to enforce open code and open data. There are other technical ways to do that, but none of them has been found to actually work in reality.