I also don't think cardio had nothing to do with JDS performance. He was hit with several bombs which prevented him from being effective in any other area but surviving.
JDS has only one thing to adjust. Only one. He needs to find a way of protecting his face while defending TDs. More combos will be wellcome as well, but if he can protect his face, that will do it.
As mentioned before. Cain wrestling alone is uneffective to take JDS down and keep him there. It's pathetically uneffective against JDS, TBH, even though he is a powerful wrestler and Cain realized that in the very first round, smartly and successfully changing his game plan to hit a surprisingly defenseless JDS to dazziness and then, only then, having the advantage to rag doll him.
And during this ragdolling, even more incredibly powerful clean shots were landed and JDS went nowhere.
Greatness is difficult to reach and deal with sometimes. I think JDS entered overconfident for this match and didn't prepare for possible variations. I personally found him a little cocky during the weigh ins (normal stuff, but maybe not used to see coming from him), promising to knock out Cain as he would just pass through him like the first time.
This loss will be good to him.
I will support your good point regardless of our differences.