Whilst he hasn't done a rebuild the way Fergie did (several times) he's managed to ensure City remain competitive despite losing Kompany, Yaya, Silva and Aguero (arguably the greatest 4 players in their history).
The squad is in such a solid position that it only needs small tweaks each season (they are a striker short), even if Pep moves on, the next guy won't have to do a huge amount to the squad.