It's not even similar. He can fail to win anything with Barca for the rest of his career and he will still be our greatest legend. However, if he fails to win anything with City their supporters will turn on him for sure! He can easily damage his legacy if he fails in Manchester.
Well he gets criticism more in Argentina and gets criticism for not moving out of his comfort zone, Barca.
Damn if he does, damn if he doesn't. So rather than be surrounded by yes men in his club all the time, and play with the most broken team without without a proper striker or wingers and a team that conceded 8 goals, i think it's still best if he moves on. PL can be physical but it's still good to raise his physical threshold than face comfortable minnows in La Liga. The only thing that concerns me is his stamina and fatigue level, to rotate often is key and thats what Pep does alot and rest him for big CL matches.
If he gets a considerable amount of goals, I think it's still considered a success whether or not he does win a title.