They do have average at best point guards, but that's nothing new for the franchise. For many years, even back to the Ralph Sampson-Akeem Olajuwon "Twin Towers" days, they never had a strong point guard to lead them, and they suffered because of it. Not until they got Kenny Smith did they have a decent point guard there.
Yao is, with the exception of his rebounding, a solid center. As I said before, rebounding is the key for being an effective center though. Until he gets stronger on the boards, he'll never take the step forward to being among the best. Besides that, considering his shooting ability (especially from the free throw line), passing ability, defense, and mental toughness (he has NEVER backed down from playing any of the top centers and has always given them trouble, Shaq included), he's right up there with any of the top centers now.