I think Jose has done considerably well considering the players he usually plays. Just take a look at Khedira and Ozil.
Bayern could have bought Khedira before Madrid but refused as they thought they didn't need him. Some would say a mistake but he really wasn't exactly a world class player was he.
Ozil had a poor season in Germany. Now, he did have a good WC but that's international football. Even Podolski and Klose looked awesome playing for Germany. Not few of my friends from Germany are surprised he plays for Jose in starting 11.
You also might want to look at Chelsea reject Carvalho. I don't think there were many who thought all 3 had the quality to slot in Madrid first 11. I don't necessarily think either of the 3 would make it if it wasn't for Mourinho.
Who is left? Ah, the 4th Mou's signing Di Maria. This guy came from Portuguese league and that's always a gamble. He turned out to be the best signing of them all.
That being said 3 of 4 of those guys are youngsters and will only grow.
Pedro Leon and Canales could be labeled as bad signings but in truth they didn't cost much and they are youngsters as well so who knows what'll happen.