I'm fairly sure Saunders himself has subbed people from rubber guard. I think his omoplata was set up from rubber guard.
However, it's true that I've never seen rubber guard work against truly elite level bjj... However, it's also true that I've also never really seen someone with truly elite level bjj use rubber guard, so it may not be a fault of rubber guard as a system, as much as it is an issue of general grappling skill of the practitioners.
As per usual, Moraes elite fundamentals broke through all the fancy shit Saunders was trying. "Basic" BJJ pretty much always wins out.
Pressure - Pass - Sub
Classic.