In "Pairs" and "Lone Wolf" leagues, matchups winners and losers are determined based on which of the two teams wins more categories. That said, "Variety" is counted as a "half category". So, for example, if Team A wins Days and Cardio, and Team B wins Strength and Variety, Team A would win because they would win 2 categories (Days + Cardio) while Team B would win only 1 and a half categories (Strength + Variety). Think of Variety like a tiebreaker, of sorts.
Why is Variety worth less than the other categories? In short, because it is a less important to one's physical health than the other three categories. Consistency (Days) and a balance between Strength and Cardio are critical components of a health exercise routine. Variety on the hand isn't NECESSARY, it's just recommended as a means to keep you motivated and having fun!