I guess my point is, and I'll use Weidman as an example, he would have more than likely lost, if he faced Machida when Rashad did... And alternatively, if Rashad faced Machida when Weidman did, Rashad may have had a better shot. The unknown is tough to overcome [Especially against a skilled opponent].
Machida has definitely declined, but the fight game is also about holding your cards close to your chest, especially as a champ. Once a weakness is revealed, it's hard to correct, especially in MMA, because there will always be someone with a career BG in the skill you are weak at.
Anderson is probably the best case of a guy who defied his weakness for a long time. He was known as a poor wrestler forever but his BJJ off his back limited the damage.
The key to Ronda, and you probably hit the nail on the head in your first post, is that her plan B shouldn't be striking. It's just not her forte and never will be. Her plan B should b wrestling, but as you've said, her knees are shot, and that might make things very difficult for her moving forward.