When I'm between 120 and 125 pounds, I'm a whole lot better climber than when I was 145 pounds. No question.

I can't really say that I'm a better climber because I'm lighter or because I'm riding more. For me, when I ride alot, extra weight does not stick around. I cannot do a controlled experiment that would entail alot of riding/training and being heavy; my body just doesn't function that way.

To the OP, focus on riding alot and climbing and intervals. You will become a better climber that way. Just ride.