Diana is delighted to spar anyway, pretty much without fail. It's not about winning or competition, not when there's no challenge or question of the outcome if she went all out - it's just a really fun thing that she likes to do with her friends, like getting lunch at a good coffee place or taking a walk in a pretty park. That's how you know you're an amazon, when fighting is as natural as eating and you do it with the same range of attitudes and reasons.
That attitude is so common in Shoenen Manga that it's hillarious seeing that the only equivalent in western comics comes from Wonder Woman.
The fanboys shouldn't be arguing about Superman vs. Goku. They should be discussing how much awesome fun Wonder Woman and Goku would have sparring!
Diana's reaction here actually says something kind of impressive about her, if you think about it. She is, after all, an incredible diplomat - it's as much a part of her definition as bending steel - but she doesn't really do deception or emotional manipulation any more than the average superhero uses a gun.
This made me rethink my understanding of Diana and gave me somne WONDERFUL ideas. First it created a problem of "If Diana won't use lieing as a tactic, then how can she take over a Superhuman policing/spying agency?" and then it hit me: by being Diana, the only person everyone trusts.