Jeremy:
If you are feeling like your legs need an easy day after your resort downhill skiing then it is definitely having a training effect. This could be for a couple of reasons that I’ll get to in a minute. But first: Even though your HR is elevated, that fact that you get specific muscular fatigue indicates that this is mainly having a strength training effect. It’s an ME workout that is exceeding the endurance limits of the FT fibers. I would for sure include these down hill skiing days in the training volume. How much to log? Just be consistent so you count the volume the same each time you do this type of workout. I’m sure that you can ski easily and your legs don’t get tired and more aggressively and make them burn and beg for a rest. That intensity factor is going to be mainly subjective as to how you log it.
It may be that you need to do more of this downhill skiing regularly to increase your ME for this sort of thing. YOU might find it benefits your touring by making you better (technical) and fitter (specific ME) on the downhills in the back country. Six days a year of this type of workout is too infrequent to have much of a positive training stimulus.
I hope this helps
Scott