The thing is, he probably would never have become that player without the shenanigans of the 2006 World Cup. That focused him into being the best he could be, without that he probably would be at Madrid, but more along the lines of what Robinho was for them, than what he is now.
Whats more, Guardiola hasnt shown anything like the capacity to replicate what he did with the La Masia graduates, to the players he buys. I really do think this will be a Zlatan MkII, only worse because with Zlatan you could see the need for him. Sanchez doesnt ostensibly look like he could add to the dynamic in any of the front three positions. He dribbles extremely well, yes. But the rest of his game isnt on par with either Villa (Finishing, and general movement) nor Pedro (intelligence, cunning, vision), and he is nowhere near on par with Messi. He is an outstanding prospect but at the moment, that is what he is. He certainly wont instantly take up a starting position for Barca, despite his price. Just look at Chyrgrynsky who cost 25m and almost immediately sent back to Shakhtar...
Its a strange move for both Barca and Sanchez IMHO. They have a need for midfield reinforcement as Xavi realistically has 3 seasons left at the top. He already seems to be passing on the reigns to Messi in being the fulcrum of the side anyhow. Sanchez will not solve that. Fabregas will, and Rossi has the cunning to operate the Iniesta role perfectly, leaving Iniesta free to take up Xavi's mantle. Sanchez just seems like overkill.