No one is claiming he is. My point is that Utd's style of play wouldn't suit Alonso, so he wouldn't be able to play to his strengths. No one would claim Nicky Butt was close to Juan Veron, but one of those worked in the Utd midfield and the other didn't. Alonso plays at his best when he can be a pure deep lying playmaker, playing next to a ball winning midfielder (Hamman or Mascherano for Liverpool, Pepe or Diarra for Real) and with an attacking midfielder in front of him (Gerrard and Ozil). If we stuck him in a 442, he would either play alongside a ball winner like Fletch, or a more attacking player like Ando. If he plays with Fletch, both of them would be way to deep and there would be a big gap between midfield and attack, like when Carrick and Scholes played together last year, and he'd have no one to pass to. If he plays with Ando, then Alonso will end up doing much of the defending and thus wouldn't get the ball in the right positions to truly create. In either situation, you wouldn't see the best of him, and without giving him the chance to play the great balls he can do from deep positions I don't think he would be able to play at a much higher level than Carrick.
That would work, but we'd need Messi and Ronaldo on the wings to really get the best out of the system