> If you are doing FP on the other hand, at least change always results in new objects, with structural sharing at most. This excludes a whole category of bugs.

Not if you program it with a mutable god object to mimic creating a new big state, then you have exactly the same kind of issues.

The issue is if you try to program a transaction flow using object oriented programming, that is not very good, and most work programmers do revolves around involves flows. But when it doesn't then functional programming isn't a very good or reliable solution.