Accumulating vertical aerobic volume is a good thing for any of the mountain sports we cover. However doing too much of this can leave your legs pretty hammered. If you are doing most of your vert on a treadmill this hammering effect won’t be so pronounced because you do not have downhills. This kind of stock plan has to cater to a wide spread in individual work capacity. When we design these stock plans they need to be a compromise and take a middle ground. The flatter runs are meant to allow for some recovery from the hilly runs. If you are handling the vert well then I suggest you keep that up as it is more specific to the event you are training for. If on the other hand you find that your legs are getting really worked from all the vert then you may need more flat recovery runs.