I agree with the notion that you can ski as hard or as lazy as you want to, although some terrain or conditions will take more effort than other terrain types.
Personally, I enjoy some speed and I enjoy some g forces, and I enjoy moguls. Mix the 3 and I find I'm in the high energy output mode.
I can get down a bump field using less energy, but it isn't nearly as much fun.
Case in point: the afternoon of a powder day here on the east coast. The trail is mostly tracked out, and almost all the skiers have skied out all the troughs of the pre existing moguls. There is still fluffy snow, mostly unskiied on the tops and backs of the moguls. I still have a great time on that run, skiing across the troughs, absorbing the bump, and turning in the soft snow on the top/back side. When you do that, there is a huge difference in the drag on the skis between the slick troughs and the knee deep tops. You have to change your center of gravity/stance from more centered on the slick to more forward and more effort to resist the increased drag of the deep snow. Each time you hit the pile of soft snow your legs want to slow down and your body wants to keep going. It takes effort to push the legs forward as you hit the deep snow over and over. Then there's the effort it takes to absorb and extend on each bump, and the jarring slam you take sometimes when crossing the trough. When I do this, I'm breathing hard and the blood is pumping hard. It feels like sprinting up a staircase. But it's a blast, and I'm grinning ear to ear.
I've skiied all my life, and I have noticed that I really never get sore, not in the sense of the day after sore/stiff. Not even on the first day of the season. I get intense quad burn while skiing (if I ski hard), and as the day wears on my recharge ability fades, but I don't get any lingering soreness. Afterwards I just have this warm rubber legs feel.
When I first started running in High School, I did feel the day after, make that even several days after type soreness. My calves were like solid unyielding clumps, and I walked very stiffly. So it's not that I have any special physiology, it seems more like conditioning, and perhaps many years of conditioning. I have a ski buddy that competes in tri-athalons, and he remarks on my endurance. I don't think I could ever keep up with him in a tri, but for some reason I'm his equal or better on the slope. He thinks it's the years, and the ski intensity at a young age (that developed a lasting muscle mass?) combined.
I think we can agree that proper technique results in more efficient skiing, and less tiring skiing. The less thrashing around you do, the better. Howver, if you enjoy G forces in any fashion, you will have to pay the piper in expenditure. You simply cannot stay flexed in 3 G's and not exert more energy than at 1 G.