[msla]

OOP is how large-scale procedural programs are organized. It allows programmers to try to reason about medium-scale parts of the system. (Mesoscale programming? Is that a thing yet?)

FP is a set of guarantees (maybe even enforced by the compiler) about program behavior which enable optimizations, for the compiler, and reasoning about small parts of the system in isolation, for the programmers.

Enough FP can allow you to abstract away the procedural parts, but even a little FP in a procedural codebase can be a good thing. Ditto a little OO, which is why C programmers reinvent bits and pieces of Smalltalk every so often.