He also gets 50% more rebounds (offensive and defensive) and 50% more steals and almost three times as many blocks per 100 minutes. He's also shooting over 42% from three point line (which is actually where I intuitively gave Ant the edge, not looking at the numbers, probably because of the games where he's been SO GOOD sticking in my mind).
I'd say Powell is definitely a better player than Ant right now, although I suspect and hope Simons will surpass him by the time he gets to age 29.