It’s definitely a fudge factor when recording downhill skiing using TSS.
In the past, I would adjust the TSS per minute of actual skiing time. On a family ski day, I found that six minutes of activity per hour was the norm; with really aggressive friends, 12 minutes. (25 minutes per hour sounds grossly optimistic.)
As far as TSS, you’ll have to adjust it by feel. In the past, I’ve used 1 TSS/minute for family ski days and 2/minute when skiing with friends.
It’s definitely more of a strength session than anything else. It wouldn’t make sense to record the total time or distance, although the total descent over a season is probably worth tracking if downhill volume is important.