Look, this isn't even just a STAR TREK thing, or even a woman action-hero thing. Movie and TV fight scenes are almost always going to be "unrealistic" because Hollywood is seldom going to want to mar the movie-star good looks of their leading men and ladies.
So, yes, Kirk or whoever is going to constantly get hit and kicked in the face during all-out fistfights, but Shatner is not going to be sporting a black eye, a fat lip, and broken teeth for the rest of the episode -- because nobody wants to see that. See also people in movies getting tossed through windows, thrown down stairs, and then springing up ready to fight afterwards. (Aside from maybe a few decorative cuts and nicks that won't stick around fro long.)
Chapel can fight Klingons without getting her face messed up because it's a TV show, and they're not going mess Jess Bush's good looks any more than they would Shatner's back in the day.