Assists comes in all shapes an colors. If the ball deflects off your foot and then another player scores, it's an assist. If the goalkeeper saves your shot and another player scores from the rebound, it's an assist. Corner kicks and freekicks that aren't particularly well taken but ends up in the back of the net, are also assists.
My point is: Rooney would probably not have any less assists playing as a main man. And if he did, then he'd probably just compensate with more goals. That's the type of player he is. Target man or "deep striker": it makes no difference. He offers the same thing: goals/assists. What he doesn't offer though, is creativity, quick one-two's, quick turns etc etc. He has a tendency of passing the ball out to the winger and rush into the box, go for a long shot(which ends up in the back of the net 1 out of 10 times), or simply lose possession. But that can be forgiven, because of all the goals.
Why not add creativity to the game AND keep Rooney's goalthreat? That is the point I'm trying to make. Whether you like it or not, a player like Rooney in the hole means less creativity. That's why You don't see any other players like him in the AM position for the other top teams. Had Real/Barca/Chelsea/Arsenal/Bayern/Dortmund etc signed Rooney, then they'd never play him as a no.10. He'd take the striker position immediately. And if he failed there, then he'd either be placed as a wide forward or on the bench.