It is not a spite thread at all. Mantis isn't simply a martial artist. She is a martial artist on a cosmic scale. She incapacitated Thor with a touch. It isn't a matter of her punching that Hulk with brute strength. She knows the frailties of a body even of the Hulk's stature. You'll notice that the debate hasn't raged around her abilities to do this, it is about whether she could get close enough too, or if the thunderclap or another means could prevent her.
If he could actually manage to touch her...before a few well placed nerve blows knock him out like she did Thor perhaps, or perhaps her empathy can help her to calm him, thus reverting him to Banner...
Of course the Hulk could easily beat her if he gets in one good blow. But she has a good chance too based on her skill set. Then let's not even begin to talk about the more powerful Celestial Madonna Mantis...