He's simply being deployed in our current tactics. I don't think anybody expects him to be a definite starter next season, it's just for the past 2-3 seasons we've had zero pace in our attacking third. Rooney, Zlatan, Mata, Van Persie, Fellaini its all very slow.
Lingard is an intelligent player who takes very little glory himself but instead drags players around the pitch because of his pace and acceleration, which frees up Rashford, which frees up holes for Pogba to run in to. Lingards performances on the pitch are very underrated because he doesn't score much, doesn't do anything particularly eye catching enough, but he gives Mourinho a solid 6 out of 10 in a role that he needs performing this season.
Next season we will have some new, better players and as a result Jose will formulate a slightly different tactic, but right now Jesse plays his part in our attack, and our attack is creating chances.