2 striker formation. He assisted almost as much as he scored. Also helped that his partners in attack all could score so he didn't have to. Bacca's job is just scoring, doesn't have to worry about anything else that Ibra has to worry about, and he's still not doing his job as he should.
When you're alone up front against two (or three) central defenders, they can deal with you a lot easier. It doesn't help that Bacca can't really be effective drop deep, which is a great way to deal with this problem by forcing the defenders to decide whether to track or stay back. He is lethal when he has space. Only way he can have much space is if another attacker occupies the spare man, which is why Bacca always looks MUCH more effective when Lapadula joins him.
Lapadula alone up front has the same problems. It's not an issue of who plays, its the fact that when their defenders have a spare man it will always be difficult for whoever is our striker.
The problem is that when you give up a player to have two up front, you lose your own advantage. 4312 is extremely vulnerable on the flanks. 442 is vulnerable centrally. 352 is a great compromise but hard to pull off unless you have the right players, but our current great advantage is our wingers and for that we force them to play wingback.
If we keep playing 433 Bacca will always suffer. Doesn't mean he's crap. The system punishes him. He could do much better for sure, but play 4312 and he'll double his goals easily but it will break the team.