Epic is more flexible since can pick 1-7 days. But there are reasons it makes more sense if can use the Epic Day Pass for 4-7 days. Given that Epic resorts are going to require lift access reservations, that's another reason to consider a Day Pass besides the discounted cost per day.Kind of like the IKON has 4 days for $399 I think I heard.
There is data that shows that 4 days is an average number of ski days at a destination resort for a reasonably large segment of the people who plan a ski vacation only once a season. Even if they fly out west, these are people who don't ski enough to ski more 5-6 days in a row. So they need an off-day. Destination resorts with non-skiing activities that require tickets like that type of guests.