Wings are suspected to be the feathers of Ducklett and or Swanna. So my explanation is this:
Not all wings can be used. To be precise the pretty wing. This is assumed to be a beautiful wing that would likely be given to graceful feathered Pokemon: Reshiram, Swanna, Togekiss,..
As for the other wings, they are probably configured into liquid. Druids used to also mix wings into potions and elixer to make energy, vitamin drinks for their tribe. This would probably also be the case to utilize the power wings on unfeathered Pokemon. Feathered Pokemon will likely have the wing put in between their other feathers as an accessory and would give them a moral boost to up their stat.