Before Azzarello had Diana personally trained by the God of War, the easy answer would have been Diana was less aggressive.

As had been stated by a variety of different writers, although Diana was brought up in all elements of Amazon culture, including warfare, she was the only Amazon who did not have any first hand experience at it. She was the only Amazon born on PI after the Amazons had been removed from the Man's World culture. As such all of her knowledge and expertise was theoretical until she actually left the island and became Wonder Woman. She didn't have any first hand experience with real violence against another person until then. Just sparring and training with her "sisters".