Always find it really odd when people say Pellegrini couldn't have done the job Mancini did. Pellegrini's record in terms of taking sides from a very low base and turning them into CL teams is how he built his reputation in Europe. I would suggest at the very least he would have had similar results to Mancini - just without all the bellyaching and drama and histrionics. He probably would've been better in the transfer market too. Mancini bought a lot of players with little thought as to how his team were going to play.
Like who? Mancini bought silva, Yaya, dzeko, aguero, boeteng(despite being a flop but is now one of the best defenders), de Jong.