Not sure why healers would want to regen pre-pull. Pre-pull regen puts you into combat immediately, which means you miss out on the out-of-combat MP ticks while traveling.

Mob spacing can make it impossible for the the tank to keep threat off you 100% of the time, and if he needs to backtrack, he will take more dmg than necessary as the distance between him and the trailing mobs will close.

Direct heals are much better for mid pull healing. You can ensure the heal goes off at an appropriate time and stay out if combat until necessary.