So you are of the opinion that Luke is a liar when he repeatedly states he's a pilot over the course of the film and never flew a T16 before joining the rebellion as he claimed.
I can't necessarily speak for JoeZhang, but I can say that that there is a big difference between a bush pilot and a fighter pilot. Yes, Luke flew his T-16 on Tatooine and took potshots against rodents in the middle of the desert. If you listen to the Radio Drama, it suggests that he "threaded the Stone Needle." Fancy flying for sure. But, nowhere does it suggest that the sands of Tatooine had turbolasers shooting at him. Nowhere does it say that Biggs, Windy, Deak and Fixer were practicing dogfighting against him or that one of them was some sort of a secret Sith Lord.
I get that the idea is that its a fairy tale and that he uses the Force to help him through all of this, but if one were to look at this realistically, Luke Skywalker would have been killed in the opening salvos of the Battle of Yavin, forgotten to the history of the galaxy far far away and the Rebellion would have been destroyed. It doesn't lessen the movie to suggest that. Its just a point of fact.