I can completely understand if people feel that Memphis has to improve and criticize him for his current performances. But I can't agree with opinions that he should be used as a sub with Young or Pereira starting at all:
Firstly, Goals/Assists in European competition do matter - he hasn't just looked good against Brugge, he was also our best player against PSV. Does that not matter? If scoring against european teams was so easy, other players would also do that and hence comparison across all competition is best way to judge attacking talent. In fact using PL statistics is an arbitrary division given the quality levels in European games was the same if not better.
The difference between his European and League performances has been enormous, but we faced much easier opponents in Champions League so far. The problem I see with Depay is he seems to be getting worse with each (EPL) game, maybe it’s in his head but I really don’t think putting so much pressure on him since day one in Manchester is working. He had in my opinion his worst game vs Sunderland, and it doesn’t get much easier. The assumption that if he did well against Brugge (very poor) and PSV (poor and we should’ve won easily) so he’s going to do it in the league is wrong IMO, although quite a popular one on the Caf.
Second, if we had a Di Maria or other superstar being benched in favour of Memphis, these points would have made sense. But he is keeping out Young, who for all his efforts, is an average player. Young got 2 goals and 5 assists in the whole last season, which is not much different compared to Memphis' PL output. That is not accounting for the fact that Memphis also had a shot on post resulting in a goal against Southampton which he didn't get credit for. This is further not accounting for the fact that Memphis has usually been marked by 2-3 players whereas Young has been afforded much more space (partially due to the fact that he has often come on from bench). Young hardly performed when started in the first match against Spurs and there were desperate calls by fans to move Memphis to the wing. Pereira is likely to be even more inconsistent, and didn't really do well even against Ispwich, which is being considered beneath our level by some people here (not holding this against him - he is young, similar to Memphis).
I get your point on Di Maria. I’m actually more concerned about Pereira who to me looks like a better prospect than Memphis, but I admit I generally prefer his style.
There were calls to move Depay to the wing from day one, because he never really looked like a player who is comfortable in the middle.
But the most important is this part:
Third, moving away from statistics, Memphis has clearly been one of our most important attacking player, even in the premier league. While Rooney has been poor, Mata can work best only when the penetration is provided somebody else. Remove Memphis and the quality of our attack would go down by a lot. I don't get how people can't see this.
Well, I strongly disagree with you on that. I don’t think he has done much in the League games. His dribbling is almost non existent for somebody who was called a winger (I noticed people tend to call him “attacker” recently), his passing and close control is poor. He doesn’t cooperate with his teammates at all, the more he struggles the more he tries to do everything on his own.
What he truly is great at is movement and crossing, he’s also quite good at long distance shooting. Comparing that to Pereira who has much better close control, and is also excellent crosser I don’t think there’s much between them.
Memphis IMO isn’t the main reason why we are top of the league. I believe we would’ve done it without him. I believe he’s a talent, but maybe he isn’t ready to be a starter here.
Fourth, and most importantly, Memphis is clearly one for the future who should be given the space to grow (and he has been showing signs of progress). With a bit of pain, we could be set for a long time with a real quality player.
He needs playing time obviously, I’m only questioning if he needs to start every game, especially as we have Young, Pereira and possibly Martial who can do a job on the left at least as good as him.