Good point, Dr. Z. He probably didn't want to be up staged, especially after he had just lost his only chance in hundreds of years to rule Hyrule.
Now, as for the Ganon wiard thing, Ganon did actually use some magic, just not while battling you. He created the storm, the barrier between his tower and Hyrule, and he created Phantom Ganon and all those other monsters.
He just didn't use magic in the battle because, as stated, they wanted the battle to be different. I think they did that pretty well.
Finally, the beer belly. Regardless of whether it's fat or robes, it's just to show his transformation from a Gerudo theif to an evil wizard. As for the jumping, remember, Ganon HAS shown that he can levitate (
OOT Ganondorf battle). I don't think jumping would be hard for him, even with all that extra weight.