Depends entirely on how much time you’ve spent on it. In my experience people become pretty good after 1hr of lessons every week for 3 years (and pretty low intensity training at that), so I imagine you can condense that into 6hrs of lessons every week for half a year.
Distributed practice is a lot more effective at teaching than massed practice per hour[1]. You might need 12 hours a week, double the number of actual hours of instruction.
Are you really learning the skill, or are you sampling it? One semester is maybe 40 hours of instruction. Even twice that in practice puts you at 120 hours. I hardly think that is enough time to become a good skier, etc.
40 hours of skiing is 10 4-hour sessions. For a young adult in decent physical shape and with good instruction, that's enough time to establish a base of technique and confidence.
That's pretty much all you get in most undergrad courses anyway. It's usually an intro to, or first taste of, a sophisticated subject that would take a long time to master. It's only after many such intros (i.e. many hundreds of hours of study) that the student will begin to develop a more sophisticated understading of their chosen field.
In that light, is a 1-credit skiing course any different from a 1-credit astronomy course?
People are different. I knew a couple newbie ballroom dancers who picked it up incredibly fast. But they were one in a few hundred. Ballroom dancing looks natural, but it isn't. Every move works against natural body movement. It takes a while.
For example, when walking, one sets the foot down heel first. With ballroom dancing, it's ball first.
By learning it I mean being proficient with it that you're smooth and comfortable with it, and can make your partner look good.