Agreed. In the right system a player can be lot better. There are different type of strikers, and Dzeko is not suited in the system City plays.
Probably that is the reason he would be better elsewhere because his full potential is a lot more than what he can achieve here.
It's bit like putting Crouch to Barca where he would have to ace in passing on the ground, to change position with Messi constantly etc. He could be OK (he wouldnt:D), but nowhere near his best potential what is at a mid table club heading balls in and fight with his monster body against defenders.:D
I would sell Dzeko, I love him, good guy, but he would be better at a club that is ready to change or use tactics to get the best out of him, and we would be also better to play a striker in his place in City with better skills suited to this kind of tactics we play.
Also Dzeko is confidence player, in rotation he is nowhere near to his best. If we could get the money we paid for him from Bayern I would sell him. But for 20m no. He worth much more, if that Gomez can score in that league 30 goals also missing huge number of sitters Dzeko can do the same with support from flanks, crossing coming in always from the likes of Ribery, Robben...
(And a less dominant partner like Muller.)