"Is my thigh pinch a beginner/intermediate technique that I need to move beyond?"
I think yes. Even without a dropper, if you spread your knees away from the seat instead of squeezing it, you can tilt the bike side to side independent of your body, especially useful for leaning the bike into turns. Also makes it easier for the bike to move vertically while your torso stays roughly in place (with your legs absorbing the bike movement). IN both movements, getting the seat out of the way with the dropper gives you more room to work with.
It definitely feels less secure not to have that contact point with the seat, but once you get used to it, you can really smooth out your riding and corner more confidently.