I find carving more demanding of fitness than skidding. Leaning back, crouching and other technical flaws in your skiing can contribute to fatigue but I don't think skiing at a higher skill level will necessarily solve this problem. I take lessons and have pretty good technique but I get fatigued easily.
Buddha, maybe you are skiing more dynamically and faster than you used to. This takes more strength. Since you are now tiring in a shorter time than before, I don't think it's your technique, unless you ski worse now
I think morphology refers to bady type (ectomorph, endomorph, or mesomorph) somewhat predetermined by genetics. Maybe a bit dated theory, but I'll claim that excuse. Fitness on the other hand is something I can improve, so I'll take the blame there.
Buddha, accept your limitations and enjoy the skiing. Don't stress about it. Do what you can to get stronger (gym, weights?), improve your skills to make skiing more fun if not less demanding. (Be safe and) Have fun!
I wasn't kidding about snowboard being less fatiguing and telemark making your legs really strong. If you are already invested in alpine skiing, stick with that I guess, but nothing beats a half day of telemark skiing followed by half day of snowboarding. Just loads more fun and better for you.