I do not agree that he is, but he is close. It is important to remember that other centers may be more talented, but not as VALUABLE...there is a big difference.
A good test is to honestly guess if a sane GM would trade other centers for him straight up. The centers who good GMs would not give up for him are: Howard, Duncan, Gasol, Bynum, Noah, Nene, Bogut, B. Lopez, Biendris, Horford.
Since no one wanted to give Shaq more than an inexpensive contract this summer, it does not seem logical to list him as more valuable or "better" than Perk. He may be a good enough fit to bring a banner, but that does not mean he is a better player.
My question is, and I think this is important...will Perk continue to improve or has his talent level reached its ceiling? Although I would expect his mobility and athleticism to get better over the next few months ( as is usually the case post surgery), I wonder if he can take his game to another level.
I would also have concerns about his shoulders. There is an injury history there that (IMO) many have overlooked during the past few days.
There is a good chance that Green can get to another level.