Tanks used to do enough DPS to carry the DPS; however, SE nerfed that.
Now it falls on healers to DPS more to carry the DPS.

Alright, now that this joke is out of the way...

In all honesty, the boost to VIT values across all tanks has created a greater amount of buffer for healers. They are able to stay in cleric's longer (as you saw) because the damage coming to the tank just doesn't match to the HP.

The exception to this, of course, is tank busters - but eventually, even that will hit a point where we have too much HP and the healers can be a little neglectful during it.