Problem is that many mechanics will just kill you immediately even at full health.

Get hit by a heart and you get stunned, AoEs will spawn under you and you will die.

Get hit by a bee and fly in the wall, get hit by another bee before you can move away and you will die.

The room for error is basically zero in many of the new fights. Especially in the more chaotic ones. And when you make one little mistake as a healer you will likely cause a wipe.