He touches the ball less than just about every striker in the league. Even players like Maccarone or Toni tend to have more touches than he does. And yes, he plays on the shoulder of the last defender, but it's not like opposition defenders are terrified of what he is going to do. He doesn't get double or triple teams every time he gets the ball like Dybala or Higuain or something which drags defenders away from other players. Teams are not scared to play a high line due to his exceptional pace, and he doesn't exactly have the ability that Inzagi had to simply always be in the right place at the right time. People like to compare him to Vieri, but he doesn't have the strength to bully defenders Vieri had. Something else he doesn't have is balls. You won't see him put his health on the line to get on the end of pass like some attackers. He's an exceptionally efficient finisher and a quality striker, but is that really enough for people to kick up such a fuss about him. He scores 22 goals in the league when he had the entire side playing for him. However, I believe football has moved on from the point where a "big side" can just rely on giving a great finisher enough good ball to win the league at the expense of having a well-rounded attack. Especially when that finisher needs near perfect service. Which is what Icardi asks of his teammates most of the time.
Just to be clear, I think Icardi is a very good striker. I just don't think he's the type of striker you win the league with, and for this reason I don't care if he leaves. Of course, I also think winning the league isn't a goal we should be aspiring to next season either.