My issue with players who relies on just athletic ability declines faster than someone like Duncan, Pierce. Dwight doesn't have the same fundamentals, his post moves are based on athleticism and he doesn't have a jumper. Same could be said about defensively but I don't think he will regress there as fast.
When he that happens he will be a huge liability on our cap and roster at the later years of the contract. I don't know when this will happen, but it will be based on how he perform this year.