It is a little crazy making that you can be great at one sport and still totally suck at another one that's sort of similar.
Both cycling and skiing are very quad intensive. The difference is that in cycling you're not keeping the quad flexed for nearly as long as you are in skiing and that seems to make all the difference. I rock at Indoor Cycling now. One of my instructors noticed that I was particularly fast and intense yesterday. If I had been thinking on my feet, I would have said that I was compensating for doing so poorly at Tele Skiing, but I just instead gave this slightly embarrassed laugh and told her (truthfully) that it was more a matter of figuring out which abdominal muscles to relax which cuts down on the bouncing you can get at high pedal RPM (while giving her credit for that discovery as I would have never figured that out by myself.)
But I am feeling stymied. I've paid my dues. I'm at the gym 3-5 times a week. I do indoor cycling and group weight workout classes among other things. I'm in very good aerobic shape. And still I struggle at times. I guess that's a "welcome to life" moment. I guess the message is enjoy what you're good at and keep trying on what you're not.
One really nice thing is after the skiing clinic, my legs have recovered and are even stronger than they were. Now about that endurance...