Are you seriously trying to suggest Martial etc haven't had chances? According to Manutd.com Martial has 22 starts, 10 sub appearances, 7 goals. Mkhitaryan has 23 starts and 8 sub apps, 9 goals. Mata has 29 starts, 9 sub apps, 10 goals. Rashford has 23 starts, 19 sub appearances, 8 goals. Lingard has 19 starts, 11 sub appearances, 5 goals.
Tbh none of those stats are awful IMO, they're just not good enough for a team who want to play 433. For me the real problem is that the midfielders (and defenders tbf) aren't chipping in with enough goals. We should either be playing 442 and giving Rashford or Martial a run up front with Ibra, or we need to do more to get Herrera, Pogba, Rojo, Shaw etc scoring and taking some of the burden off the forwards.