Open banking (or open banking) refers to a banking system where external financial service providers have secure access to financial data through APIs . This enables the creation of account and data networks between banks and non-bank financial institutions. Essentially, it enables new types of products and services within the traditional financial system.
However, DeFi produce a completely new financial system that is independent of the current infrastructure.
For example, open banking that are allow the management of all traditional financial instruments in a one application by retrieving data from several banks and institutions in a secure way.
Decentralized finance, could allow the management of entirely new financial instruments and new ways of interacting with them.
Traditional banking basically have to be compliant and follow all rules and regulations of the state or central bank of the country they are operating as well as have to comply with international monetary rules as well that is why i think traditional banking is not that efficient, expensive and outdated.
Defi on the other hand is a concept that is borderless and without third party intervention and aimed for masses but we still have to wait an see a whole ecosystem in the defi that can compete the traditional banking.