For interface sanity, clean encapsulation and maintenance purposes use OO,
I do not think OO is more maintainable when you are comparing advanced programmers to advanced programmers.
Hybrid functional development allows functional programming with objects. Even Lisp has structures.
FP code in itself can be incredibly easy to maintain, especially because the chain of function calls is usually very short and direct ... that, and short automagical functions are encouraged.
OO does an excellent job, though, when you really can't trust everyone in the codebase. It defines boundaries, rules, and operations ... a well defined and documented API does this in the same way, though it doesn't force a design methodology on the entire codebase and through every class/source file.
