I think people vastly underestimate how much better of a shooter and finisher Morata is then Rashford and even Martial. He's much more composed, experienced and reliable in front of goal...
He may have world class teammates but you need to finish well if you are going to rack up the goals he did in those minutes, he can have some screw ups (like zlatan had some sighters almost every game..) but overall I expect him to be a success. If he isnt in terms of goals, either Martial, Mkhitaryan and Pogba have amazing goal scoring seasons, or we are screwed and need a new forward by January. I do expect we will be fine, but I highly doubt it will be Rashford that boasts the highest goals tally for us already, i think its a season or two too early for that.
I'm hoping Rashford and Martial become consistent scorers over anything, netting 15 goals individually at the least. It's actually a low standard, at least for Martial, so heres hoping I'm not disappointed.
Also people act like Mkhitaryan isn't elite on his day... He just hasnt hit form here. He was bundesliga player of the season/year (w/e it was) last season. That means he was considered better than the likes of Lewandowski, Robben, Vidal, Tiago, etc...