>>27986627Audino is good because it can take multiple prizes on the same turn. Its bench damage is what makes it very good and unique; not many other Pokemon can so easily hit the bench. That damage is so valuable that people were actually using pic related in Regionals and States to deal with decks like Night March.
Glalie just does damage. That's it. And when it comes to a Mega Pokemon whose only goal is to hit hard and fast, there are many other Pokemon that do it stronger and faster. M Ray, M Mewtwo, etc.