I'll try to explain. Rooney plays the supporting striker with Kagawa. The top striker position is occupied by 3 players; Welbeck, Hernandez, and Berbatov.
We can have Rooney playing as the top striker with Kagawa as the supporting striker against top class opposition, but for argument's sake, consider Rooney not available for the top striker position.
We played 53 games last season. Welbeck got 40 games, Hernandez got 36, and Berbatov got 21 games.
Again, forget the fact that Rooney can play there as well with Kagawa behind him. You want to add Van Persie, who can only play effectively as a striker up top, to that list of 3 attackers.
Most of you want him to replace Berbatov. That would be perfect, if Berbatov wasn't our peripheral striker. You see, our main strikers in that position are Welbeck and Hernandez, with Berbatov coming into the side only when these two lose form or need a few weeks of rest. You want Van Persie, who will be demanding to play almost every game possible, to play as our peripheral striker? That isn't going to happen. So, you want either one of Hernandez or Welbeck to play as our peripheral striker? That is severely unfair on those two players who have more than justified their presence on the team sheet as starters over the last two seasons.
The way I see it, Van Persie's arrival would severely hamper the development of either one of them, if not bad, Hernandez or Welbeck. I don't want us to purchase a stop-gap solution for 3 years if it means that our young and very promising strikers' developments will be hampered. No thank you.
In my opinion, this will be Berbatov's final season at our club, with Will Keane replacing him in the squad as our back-up striker to both Hernandez and Welbeck.
I know Sir Alex has always said he loves to have 4 strikers, but that when we played a traditional 4-4-2 with two strikers up top. Nowadays, we play with a modified 4-4-2 with the second forward (mainly Rooney) dropping deep and collecting the ball, playing the supporting striker role.
Assuming Van Persie joins and plays regularly for 3 seasons then leaves, then, Hernandez (27), and Welbeck (25) will enter their peak years without any serious first team experience for the past 3 years. Add to that list Will Keane (22), approaching his best playing days with no first team experience.
Don't get me wrong, I admire Van Persie's quality, but I don't want his presence hampering the development of Hernandez and Welbeck. In my opinion, we have enough strikers for the striker up top position.