It's very hard to "underheal" galakras
. The entire healing requirement for the fight came from the extended amount galakras was alive. When he dies inside a bloodlust, that's no longer the case. We have found it 100% impossible to rank as healers on the fight, despite 2-3 healing it, because not enough damage goes out (as an example, tonight we had: 170K from disc - 150K from r sham - 140K from hpally, which landed me as the disc priest at roughly rank 2000 out of 4600).
That said, the easy steps to a quick galakras kill:
Never let the grunt hit the door-goblins (that includes killing the grunts on the second tower whenever you see them, despite the first tower not being "done" yet).
Void tendril the demolisher and have the entire raid zerg through the towers.
Zerg galakras.
GG.