The few things I think I am "efficient" at came only through lots and lots of practice. However, there's smart, mindful practice and there's dutiful practice, as the OP notes. I can't argue with that.
Of course, for athletic endeavors there are some people whose bodies are more suited to certain ones than others. My wife is very long limbed and flexible, which makes her excellent at static movement sports like rock climbing and yoga, which she took to instantly, especially climbing. But she is never going to be anything better than a competent skier -- she just doesn't have the muscle mass or dynamic coordination skills.
Someone mentioned being light on your feet -- that's an extension of the basic 'defensive crouch," which is the foundation for almost all sports involving explosive movements, including skiing. You need to find your balance point with a low center of gravity, and if you didn't learn that by instinct at a young age, whether by playing team sports, or surfing, or skiing, it's going to make skiing a whole lot harder.
As for "down time" or "off the snow time," I've been a surfer for 35 years, and there's no way you could ever spend 10000 hours actually surfing. I might surf for an hour or two each year. (If I catch 20 waves per session, average 10-15 seconds a ride, that's pretty good). But being in the water, just goofing around -- that counts for a lot. Not sure that applies to skiing directly, but if you spend time on the lift watching others take lines a certain way, that will help.