Boston Celtics center, Has anyone ever thought about this (give me your thoughts)?

JaJuan Johnson is 6'10 and Kendrick Perkins is also 6'10 so why dont people think he can be the starting center. JJ is alot faster and leaner than Perkins AND his jumpshooting and free throw shooting is alot better. All Johnson needs to do is hit the weight room a little more. Please give me your thoughts about why or why he shouldn't take over the starting center position now that Nenad Krstic is playing in Russia, Shaq has retired , and Jermaine O'Neal is basically just getting old.