[branchless]

I've worked in two of the biggest US banks for years and I can confidently say both important departments were far from completely understood by most people working there, let alone outsiders doing an audit.

Most of the complexity is in the messages passed between systems. In a code audit it's fine to remove sending tag X by system A but then you find out when you hit prod system B used tag X and now it's not there which causes a problem in system C. And that would be a simplified example.

I'd be disturbed by any outsider claiming they understand the dynamics of multiple systems with millions of lines of code which often have feedback loops.