Nobody has ever answered the question of the competitive advantage functional programming gives apart from the opinion that "sounds cool". The principles of functional programming definitely have their place in modern development but picking the de-facto tools for a job is always the safest choice when you do commercial applications.
It's kinda of sad when people treat functional programming not as paradigm but as a solution to their problems. Sometimes I feel that they think they will let all of the bugs, design decisions etc just go away, only by using FP.
I think that for game dev OOP is a better abstraction than FP.
One of the great things about FP and Clojure in particular was that it showed me how you can cleanly separates values, identity and memory addresses.
But in games you're often dealing with memory directly anyway and don't want to abstract that away. And abstracting identity from address doesn't buy you much because you're always running in shared memory space unlike distributed systems where it suddenly makes a lot of stuff transparent.
It's kinda of sad when people treat functional programming not as paradigm but as a solution to their problems. Sometimes I feel that they think they will let all of the bugs, design decisions etc just go away, only by using FP.