From all my clients I have reached a conclusion:
Flexibility are very closely intertwined. From every single one of my clients, I've seen this over and over. Those with EXTREMELY good flexibility may start average but their progress is always astounding. They progress like lightning bulb in some cases.
Those with extremely poor flexibility usually take considerably longer to make good progress.
This is no news, but its very interesting to see this in so many different individuals consistently.
I've never consistently stretched, but now it is part of my daily routine, and I'm focusing on developing as much flexibility as possible along with strength and power.
Just an interesting bit.