Bummer.
The truth is, if somebody really wants to lose weight, they can. We saw all the pictures and quotes from the summer, but those were just quick snippets. How intense were his workouts? Was he really dieting? I do quite a bit of long distance running and I know some decent runners that don't look very athletic at all due to feeling they can eat whatever they want for 'energy.'
My guess is that he did pick up his workouts, but didn't stick to his diet, and when he went off his routine, any progress he made went out the window.
It's possible his efforts will transform to the court, but he is nowhere close to the Kevin Love transformation. If somebody really wants 'it', they will make it happen. We found out more about Sully this offseason than in his entire career so far.