Uh. What? Fully accepting the object-oriented paradigm does not make a language any more likely to properly isolate state and side effects[1], any more likely to have immutability as a default assumption, or any more likely in any other way to encourage referential transparency. As referential transparency is the essence of functional programming, this makes your claim very confusing.

[1] Following OOP design patterns makes a given program more likely to properly isolate state, but this is by no means a virtue of OOP languages.