I can’t say what will be productive 5 years from now. The push back with large functional code bases is that everything kind of turns into being a util.
I’ve been writing ClojureScript for 2 years and i’m much happier with my larger projects than I was with OOP code bases I’ve built. I lean heavily on FP as much as possible. OOP still adds value it’s just much less practical. The more idempotent and functional my code is the less it breaks and the easier it is to refactor.