Quite frankly, at this stage, who knows what tactics we'll be employing next season. There's an assumption we'll get Pellegrini as the manager, and that he'll employ more width and pace than Mancini did, but at this stage it's not a certainty. What we do know is:-
1 - Dzeko simply did not suit Mancini's tactics, if anything Mancini's tactics played to Dzeko biggest flaws and completely ignored his strengths.
2 - Dzeko, for whatever reason, seemed to give up last season. Early doors he was on the bench and was actively putting in some fight to try and change that, however the second half of the season saw a far more lacklustre and disinterested Dzeko. Potentially frustrated with a lack of opportunities, or with the tactics, or with the manager himself. Whatever the reason, it was an unacceptable lack of effort.
3 - Dzeko will never be a top class striker. Don't get me wrong, he's good, very good on occasion, but his weaknesses will never allow him to be a key player at a club like City. His passing is never going to be good enough, and his first touch too is not of the required standard. At a lower level club, the next level down, so a Wolfsburg/Everton/Sevilla/Lazio type level he'd probably be absolutely fine, but for a title contender, and a Champion's League hopeful he'll never quite be good enough.