She's also a character in an extremely visual medium, which has a language that is not entirely related to the real world. In comics, Superman is bigger, broader and more muscled than Flash. Why? Because Flash is fast, and Superman is strong. Does this make sense, considering that Clark's strength is essentially magic, and there would be no way for him to build muscle when nothing in the world is actually a physical challenge for him? Not literally, no.
But visually, symbolically, that's the way it must be, because you need to immediately, instinctively, on a pure gut level, know when you see Flash "he's fast" and when you see Superman "he's strong."
Diana can jerk the moon out of orbit. If I can't tell that by looking at her, her artist has failed.