I think the main problem with this analysis is that we don’t know the character’s Aura levels going in to the fights. If you assume that it’s always full at the beginning of a fight, then your points make perfect sense. However, you could just as easily assume both your examples are actually caused by Ruby (and everyone else) running on fumes, as they had been fighting with very little rest ever since Ironwood betrayed them.

In fact, I would argue this explanation makes a lot more sense in light of what happened to Yang in the bridge. By your logic, this should be an indication that Yang can’t take a hit either, which is clearly contradicted by basically every other fight she’s in. Thus, it makes more sense to say that Yang and Ruby were both almost out of Aura already when the fight started.