I don't think Firmino is very good playing as a striker. I've seen him play there for Brazil and he looks like an attacking midfielder someone's stuck up front. Underwhelming player.
I doubt he's ever going to be better than he is right now, but if he does then let's sign him in the future instead. I'd happily pay an additional 15-20 million for him if it meant we could avoid years of development and uncertainty.