For O3S in particular, if you Awareness+Raw Intuition the first Critical Hit, then you have 20% reduction on incoming physical damage through the first Spellblade Holy. If you're really having issues you can also stack Vengeance with it. Because Awareness+RI is so OP for Crit Hit this leaves Rampart and Vengeance up for other damage mitigation throughout the fight.

Likewise, Raw Intuition can also be used to mitigate the vast majority of the Tail Swipes in O1S.

In O2S you've got rampart up for every double frontal cleave, which is really the only heavy damage that the meatball puts out. Either you are using your mitigation kit properly and your healers are bad, or you need to reconsider your pattern of cooldown usage.