He didn't fail at City. That's like saying Berbatov failed at United. Your sentence reeks of snobbery. As if Roma were Hull. With guys like Morata, Llorente and Mandžukić having played for Juventus in recent years, he could easily have played for them too. He's probably on a decent salary.
Mkhitaryan isn't producing near to what he did last season. On current form, he's no better than Salah.
Rooney scored 34 goals during the 2011/2012 season, despite his general play being average. Ibrahimović is doing the exact same thing, which is more understandable given his age. We will not return among the elite of European sides with him as an ever present. He's a good stopgap for now, and his aura helps lift pressure from other players. But sadly, we're too reliant on his goalscoring.
I have never paid any attention to the bookmakers. Odds change overnight. Are we one of the favourites? Yes. Are we a good few yards ahead of other potential winners? I don't think so. Not with our away record.