Just put it this way:
He inherited a team that had been overhauled within the last five years that Rijkaard was in-charge, and had deployed the youth from their own academy in the likes of Puyol, Xavi and Messi to start creating a new blanket that would replace the old guard. He continued on the preferred tactical styles of a fluid and attacking 4-5-1 and put Messi into the trio with Eto'o, Henry and Ronaldinho (when they were there). With it, he has won many titles, achieved undeniably difficult feats and made Barcelona stronger. He wasn't really lucky to become the manager of Barcelona, because he was under the tutelage of Rijkaard anyway, so it wasn't that difficult a decision for Laporta to appoint him - as well as the fact that he had his coaching badges already and was tailor-made.
Guardiola is a good manager. We cannot take that away from him. Managing Barcelona is a dream, as well as a challenge, so what he has won and achieved is all taken in a good stride. But had it not been for Rijkaard and his philosophies of deploying the 4-5-1, the introduction of youth players such as Messi, and the disposal of the old and frail, we may never had seen the Barcelona of today. Can't really call him a genius, but we can't dispute that he was lucky either.