In their second duel, Rey may have fatigued quicker due to healing the monster on Pasaana. But even before it mentions that it states that Kylo was stronger, and that she couldn’t break through his defense despite going all out and trying to kill him.
In their first duel Rey was also going all out trying to kill him, but Kylo was just casually defending.
Along with the other things I mentioned in my previous post, it’s pretty clear that Kylo is her superior.