he could well be fit, some people are just heavy and extensive effort to loose weight could actually be bad for him.
as long as he feels good and fit he'll be fine, cricket's not a game where weight is going to severly hamper you, it's not like he needs to keep running at a high pace for hours and hours and being heavy will make that harder. he can stay out there a long time without cramp, he even seems to be new zealands go to part-time bowler, I don't think his fitness has been exposed. Compare him to shah who had to retire with cramps and got out with lazy running, that's fitness not being good enough.
I wouldn't back him to make a very quick single with a diving finish maybe but so what?
also the footwork thing is nonsense, it's fine, very good in fact, just he's able to play in that hand-eye style way like sehwag so it's been assumed he must also have the weak points that normally come with that.
Basically, he's probably technically the best cricketer under about 27-28 that's playing cricket right now. that's not me getting carried away.
even in australia where he was pretty poor, his main problem was shot selection. that's the easiest flaw to iron out, you just get better at taking your time and judging. if you have all the shots, and you see the ball early and play it late like him, that's going to sort itself out in no time.