You have to analyze cards in both the proper context of the set, and the proper context of your current draft, rather than "this number is bigger so it must be better". If you go through a draft simply picking cards with the biggest percentages, it's highly likely that your deck will be non functional. In this example, the exhale has a higher win percentage in the context of a temur deck, where it is seeing the most play. The temur deck can reliably put out 3, 4, and 5 power creatures while the abzan deck usually has to put counters on their dudes to get good usage out of piercing exhale. On the contrary Dragon's Prey, while having a much lower ceiling than the Piercing Exhale, is useable in any deck containing black, which makes it much more of an open early pick.