In reply to damuze:
It would be great to have it in healbot for extra info but useless with YOUR problem.
Most problems with overhealing exist because there are people who heal before you. As an example: Holy Paladins and Druids. Paladins have no HoTs so their heals arrive instantly while druids mostly heal on time. When a paladin casts a heal right after a druid did, he fills their target nearly instantly so the rest of the druid's HoT becomes overhealing. When you eliminate overhealing from the equation the problem is that though druid's heals came 1st, most of them wouldn't be counted (because on time part of them become overhealing) and they would seem to be healing too late and too much, and it would look like if the druid was a bad healer. Worst of it eliminating overhealing in that count would make the druid look even worse as the amount of healing shown would be ridiculously small (however he healed more and before anyone). The recount wouldn't show the real performance of the healers.
Of course it was only hypotetical. In BfA paladins are horrible healers compared to other healers so a paladin will never fill his target's life before any other healer. I'm a holy paladin and know it well, they've been horribly nerfed after Legion.