I wouldnt say that is a good idea. balanced crit/mastery works best in my experience, because your biggest heal is star, not PWS. You can also get PoH casts easily under borrowed time and the trinket has a 15% chance to effectively duplicate the spell, but make it smart heal. For holy it is a crazy monster, easily >10% of total healing just from the cleave, but it works well for disc to.
Siegecrafter is just not as good when the raid is stacked. 2.4k spirit is not going to net you 5-6% of total healing. Maybe 3%, but no more.