Stat had a major injury last spring, no if's, and's, or but's. It's unknown the true extent of it, but the fact that he didn't have much basketball-related activity for so long speaks to the severity.
He has long a lot of spring/explosiveness that he had last year. We have little explanation why his camp deemed it a good idea for him to pack on 15lbs of muscle vs his playing weight of last year - this on a player with surgically repaired knees with an expiring warranty.
I think his center of gravity has been off since the beginning of the season, and he's been struggling to get his body balance right. He's probably shed some of the excess muscle since the season began, thus has begun showing flashes of his former self.
With that said, Stat has probably sacrificed the most to have Chandler fit in. Amare has traditionally played more than his fair share of center. Given the state of the position in the league, matching up the athleticism and quickness of Stoudemire vs a center is generally a good thing. The thing to watch out for is him guarding the few bruiser centers left in the league. With Chandler on the Knicks, Amare doesn't have much of a mismatch on offense - given that he's spent a lot of time parked on the perimeter.
With regard to sacrifice - look at how Kevin Garnett has seemingly fallen off the map with the Celtics. A fact of life is that the Knicks now have a lot of scoring threats on the team - so moving forward, his teammates might actually provide a better chance at scoring than he does on any given time down the court. Not a knock on Amare, but as long as opponents see him as double-team quality threat, he'll be a nice decoy.
No thanks on Zach. At least Amare isn't a ball hog. Zach is like the chubby PF version of melo. Loves iso's.