Are you kidding? GJ was a nobody and able to reach Great level within a decade. Without 9 yin, I don't see there is any chance for him to reach that level ever. It's unfair to compare GJ to DFBB because DFBB wasn't a beginner like GJ was. He was among the best prior to practice KHBD. A fairer comparison would be between GJ and LPZ because they both are beginner prior to practice their respective martial art. Do you think LPZ's Bixie is better than KJ's 9 yin? I personally don't think so. GJ internal energy increases gradually as he progresses. On the other hand, I don't see LPZ internal energy increases much as all.
I don't think 9 yang is better than 9 yin. In my opinion, I think 9 yin is slightly better.Still, we might be able to attribute SPW to just being in a weak dynasty. Zhang Wuji dominated with 9 Yang as hard, if not harder, than DFBB did if you factor in their fighting mentality and experience and we don't really think of 9 Yang as being much better than 9 Yin. Give someone like Miejue full 9 Yang Power and let's see how much havoc she can cause!