If you read the early Superman stories, there's a period where Superman is doing so much in his leaps that he might as well be flying. But I think it's even better because there's a physicality to what he does as he's pitching through mid-air that you don't get with strict flying. It's more like the logic-defying leaps in some Chinese martial arts movies.
I think that's what Diana is doing. She may have enough power to stay in the air for a long time--but at some point gravity is going to pull her back down. In point of fact, that's what flying really is. It's not anti-gravity--it's manipulating physical forces to stay in the air for as long as one can manage it.