Sané and Sterling add so much more than their goals. Apart from the obvious (assists etc.), they are now the focal point of our play. Our attack goes down the wings and is based around putting them 1v1 against players they beat. Their pace and movement is creating 90% of our chances, and they're our first line of defence, pressing like madmen, sprinting back, stopping counterattacks and making interceptions in midfield.
Aguero scores goals. He doesn't create, he doesn't come up with assists, he doesn't add much defensively and he's not particularly involved in build up play.
That's why it's OK for Sterling or Sané to miss chances. Being clinical in front of goal isn't their entire game. I absolutely love Sergio, but even now when he's trying his hardest, if he's not scoring then he's not really contributing.