The problem is that neither Martial or Rashford have shown the level of Di Maria, Robben, Hazard etc to be able to go from their own half to the opponents goal.
Martial and Rashford are great when teams park the bus and they dont have other responsibilities but when they must maintain a good shape, track runners, cover space they struggle to do those things and be effective in attack.
This is the reason why we wanted Perisic; because he is a player that will defend in one instance and be at the other end of the pitch 10 seconds later.
I disagree with pretty much all of that I'm afraid but I won't get into it because I don't see what Mata on the right does wrt your post that rashford wouldn't.