Whereas Antonio Valencia clearly has some value other than attacking (where in his poor form, he's offered little...) Ashley Young does not have a single redeeming quality that is better than our other wingers/forwards. Valencia is aggressive and helps win the ball back and can give balance and help in a big match, a few of the things we picked Park for. So its worth keeping him in the games to make sure he isnt lacking match fitness when the big games come around.
Young is just a mediocre player. He is just an attacker with decent pace who throws a decent ball into the box sometimes and tries to keep it simple with his passing and occasionally pops up with a nice shot. He doesn't run at defenders, he isnt creative, he doesn't bring anything that our other players dont have like Valencia does. He's just a standard europa league winger.