I expect 15 goals from Firmino, I was disappointed with his return last season as a result, and he needs to improve. The problem here isn't so much that point, it's the fact that that's the only point some people can see, he's a good player for us, and he brings a hell of a lot to the team that makes the entire attack play much better, these aspects often get lost under a barrage of "He can't finish" which is disappointing.
We could upgrade on Firmino, but would require a very special player to be a decent upgrade. As Hansern has already suggested, we're looking at a Sanchez, a Costa, maybe a Kane, definitely a Suarez. We could slot a Defoe, Zlatan, or heck even a Aguero, and yes they'd score more goals, but the rest of our attack simply wouldn't work as a result, so it would make no sense. People need to stop acting as if it's that simple, we don't just need a "20 goal a season striker", we need a really fucking complete attacker who also scores a shit ton of goals, and they are in quite high demand.
So lets stop making this debate so binary, it's not that simple, Firmino disappointed on the goal front, and needs to reach 15 goals this season, but lets not pretend he's dreadful, or a liability, his game is about much more than that and his game was a key reason why our attack destroyed teams last Autumn.