Alves wasn't. Villa wasn't. Pique wasn't. Busquets and Pedro were B team players. Xavi, Iniesta and Messi had never played as well as they would do under Guardiola. And the core team was nowhere near as successful under Rijkaard. They finished 3rd the season before.
Messi and Iniesta were established in the team, and Xavi was playing equally well. You can hardly credit him for these 3. They were already on the upward curve and were the core of the team along with Puyol.
He then also got a fair bit of financial backing, which he didn't spend very well in the likes of Henrique, Ibra, Chygrynksy, Caceres, Hleb, Mascherano etc.. Alves has been good, while Villa and Sanchez have been OK and are hardly integral to the team.
Pedro, Busquets and Pique he deserves credit for, especially Busquets but that's not taking the credit for the whole team.
They were going through a transition period when he came there, he took that forward decently well with good financial backing but that's hardly creating the team for scratch. Players like Pique and Fabregas would have moved back there anyway, irrespective of manager too.
On the other hand when Rijkaard took over they were in complete mess, and not even that big of a draw. The whole team needed renovation with no youth products coming up either.