Sounds like a take from an individual who a) does not see the benefit or b) just does not get it.

I have refactored large enterprise systems, and always tend to write in an FP style depending on the language. Im not talking about full blown Haskell here, but traditional C like languages.

Just keeping it simple, avoiding mutation, isolate side effects and having pure functions will take you a LONG way for better software.

You dont have to go balls deep in category theory for FP, and usually the language you use is not really suited for a monadic way of things, i dont like to shoehorn that stuff in if im not working with something like ocaml etc.