As a striker they're not going to stay centrally all the time. They'll drop to link up play, go out wide (either side) when the team is defending leaving space to dribble, be in the box, etc...
He doesn't have the skills of an Alexis/Messi type player to play out wide consistently. He has great technique for a striker, but it's different when comparing him to other attackers. His finishing ability is so good that he needs to play as the 9 so he can gobble up as many chances as he can. We saw against Spurs, Wolves, etc... that he can find little space in the box and finish. Even using Sanchez/Messi as an example, they were moved centrally to get the best out of them.