EX cards with their time limit are also great tools to stir up the meta. Whenever new cards are released the meta changes a bit. From the release of Set 5 till the release of Ex 5, mid lawtia was the most popular, and in just a week half of those decks dissapeared giving place to other files with the new cards. Like this Ex packs can be used to bring change to a really static meta (or turn something balanced into static :/ ) without the need of releasing a whole new set of cards.
That being said, if this Ex pack would last 2 days longer, i could buy my 3rd Yuni without selling cards.
Something must be wrong with me. I'm giving advices to someone i should kill.