There simply was no weak link in that band. All Gods, yet still mortals in the way of flesh and blood.
Seriously though, the man kicked rump and was the glue that held the band together. He led from behind, so to speak. He cued the band on changes, always had the steering wheel and like a good Shepard, collected the flock when they wandered a bit to far, leading them back to the song.
The complex rhythms and underlying tones of songs such as Kashmir was unmistakeably JPJ driving the bus. JPJ and his musical genius allowed Page and Plant to explore with a solid safety net under them, allowing risks to be taken and history to be made.