I've done dream / fantasy teams for years and I know all too well that players have purple patches. For example, picking a random player here; Aguero. If he scored in the opening three games of the season, there is no way he could sustain that scoring rate. He's not going to get 38 league goals this season. Last year, Ramsey got a lot of goals early on as did Giroud, both have done it early on but then faded for the last couple of season. simply put, they can't sustain the scoring levels they started with.
On the other side of the coin, Rooney as started very slowly this year. However, history tells us that he averages around a combined total 30 goals/assists in majority of season. Therefore, I would have thought his slow start will get better at some point. he usually as a purple patch at some point too.
Bascially, what I am saying is MITO as picked the early form players but none of them will be able to sustain that level of contribution for an entire season. they have already used up a proportion of their contribution in the opening two/three games.