That's an overly harsh and negative assessment.
Mancini did make a few mistakes - but ultimately the players he put out against Napoli (home and away) should've won.
His record at Inter wasn't great, but then that team wasn't as good as our current squad is, and more importantly he is older and more experienced than he was back then. Ultimately he knows he lost that job because of his CL record, and I expect that will have chastened him enough to make sure he succeeds in the competition while at City.