You can always ask the tanks to do smaller pulls if you are having problems. But usually mass pull healing usually involves divine seal+regen, divine seal cure and then cure 2 spam or presence of mind cure/cure2 spam and even a benediction if needed, also eye for an eye is valuable with multiple hits. A swiftcast stoneskin can give you a slight breather as well.
The non use of tank CDs lately(or even tank stances) has also been pervaisive so might be hitting that as well. A lot of tanks also seem to expect a whm to holy spam the large pulls so they are stun locked for quite a while and get burnt down faster thus requiring less healing.
You could probably find a few whm mass pull rotations on the forums as well.