Another reason the battle is enjoyable is the weight of the lightsaber are taken into account and matches the weight of what we see in ESB and ROTJ. In the special features, the actors talk about how much they had to strengthen up their arms in order to hold the very heavy prop lightsabers convincingly. That's attention to detail, particularly the detail of lightsaber battles in the OT.
Well, that would also be the work of the choreographer not just JJ. His only job is to show something revealing about their characters during the battle, which he does. Rey runs away and Ren is still incredibly strong despite the wound.
As gusninja has already pointed out, Rey does kick Ren in his wound, which is the 1st attack that lands him on his back and right after we see him holding his side in agony. Also, her 1st lightsaber attack that lands seems to graze his wounded side which results in him holding his left arm down near his side allowing Rey to stab his other shoulder. I'd say that's doing a good job of keeping up with the impediments of Ren while the battle unfolds.
Echoed in Han Solo's reply to Rey's insecure "I think I can handle myself" is "I know you can, that's why I'm giving it to you". Whether she believes it or not, the force, like Han, is with Rey.
I don't think studio execs would be too happy to fund a movie where the main character has nothing to learn
And again, I agree about her needing to be defeated in some way. Which I'm sure we'll see in VIII and will in some way relate back to Rey's doubt.