Functional programming is not a panacea. It isn’t necessarily better than OOP.

Yes, both can coexist, and they have for decades! Did you know that Smalltalk can do functional programming? In fact, Smalltalk’s class library contains many recognisable functional constructs.

In this sense, Smalltalk is much like Scala, or any of the recent major languages that have added lambdas to their feature set, e.g., Java, Python, C++, etc.

Nevertheless, OOP remains the most widely used paradigm in the world, by far. Functional programming is nowhere close to catching up. Like I said, they can coexist, and you will find functional code in many OOP code bases, but functional programming will always play a subservient role to OOP.