Back when they first added DA to PoH to make it viable the problem of using it to stack absorbs was discussed. One possible solution mentioned was to simply make PoH convert all previous DA on the targets healed into instant direct healing and just leaving the new DA caused by that PoH behind.
This would have solved the throughput problem (PoH healing way less for Disc than for Holy with no alternatives like Holy has) and prevented excessive DA stacking. It would even improve Disc's ability to heal groups back up after heavy raiddamage not on a fixed timer, something it would currently struggle with if such encounters came back.
I think something like this would work better than just removing DA form PoH completely, which might make it too weak due to targeting limitations and lack of complimentary aoe smartheals. It's easier to balance as well. (Since there would be two more numbers to tweak whereas the version currently tested has none on the side of disc priests.)