I think you can take it as read that the Aguero-Tevez figure as it stands is an anomaly and not at all reliable. With that run-rate it'd be almost a 100 goal a season partnership. No-one has ever come close to that. Ronaldo-Rooney-Tevez, never got close to that as a three-man attack. They managed 57. Drogba-Malouda-Anelka (the three-man in the record holding 103 goal Chelsea season) managed 52.
Now part of the reason for the imbalance with Aguero and Balo, is penalties. When they're both on the pitch Mario gets the penalties (rightfully so). That puts goals in Balo's column rather than Aguero's. You have to remember that easy transfer of goals in this case. Penalties are almost certain goals and can inflate or deflate individual player's statistics hugely depending on who takes them.
The bigger concern though is why the drop-off between the Dzeko-Aguero partnership avg of 1 per game to 0.6 per game. Is it explainable simply by making reference to the period in which it was the main partnership i.e. January to March, when we were hit with many absences for reasons of African Cup of Nations, injuries and suspensions. During this period the following players were all out; Kompany (twice); Lescott; Richards; Silva (rested and injured); Yaya (twice). Could that explain 0.4, I reckon so. A goal a game is adequate from a partnership. That's about the level Henry-Bergkamp-Wiltord were at.