Because I don't think I saw anyone mention it- If they up the cast time to a full GCD or higher it means there wont be any window in-between casts for an auto-attack, which is an effective potency loss of 100 in shield and 175 in sword oath (granted resqeusghsdrhsdjnsdtr doesn't increase this damage). You lose both your wiggle room for moving around and weaving and a heap of damage too.