I've always been a spinner. At first, I couldn't even lift myself up to stand, and I really don't know why. I wasn't heavy then, nor particularly weak. About 6-7 years ago, I began to be able to stand on little rises and that is all I ever do. I can stand on a spin bike, but not very well on the trainer. Even when my bike is in a very hard gear on the trainer, I feel wobbly. When I have tried to stand on a real climb, my legs hurt so incredibly bad and i lose speed, and generally feel miserable. I look at the way my DH can power up a climb (although he doesn't always do this), it pisses me off. My son, who raced, was a "climber," too and watching him was like looking at a work of art.
I can climb quite well, compared to most of the people I ride with, so I don't complain. I may try working on the standing more on my bike with the compact, as Indy said, as I can see how being "lazy" to shift might help. But, overall, I am happy that I can get up the climbs I do, i.e. my lovely driveway and street.