hmm

Firstly, defensive cooldowns aren't like offensive cooldowns. Using more than one at a time becomes detrimental to their effect. Sure it gives more defense, but less than the skill could give alone and overall it's a waste. (only exception being foresight, as it modifies your defense and is not a %damage reduction).

Second, you shouldn't use them all as soon as possible. They are usually occasional. In a SR like Brayflox, use them all in order, sure. But in a raid or trial you want to time them for the big hits that are coming.