When you ignore all evidence given, as recently even as within the past few pages, of
the curvature of the Earth content that requires dps from healers, then sure enough,
in effect no one has shown a single piece of content in the game designed to require dps from the healers.
When you don't, however, that evidence remains. Such as even in literal MSQ solo scenarios. Or multiple Savage fights. Or, indirectly, the ToA, for which the developers have confirmed that refusal to deal damage in one's spare time is a kickable offense under "Lethargic play".
Yet, unskilled yet highly defensive players prefer to tout an almost immediately disproven errant quote from the first few years of the game in an attempt to defend for themselves said lethargic play contrary to the actual ToA.
Also: Healers dealt damage in their spare time even in 1.0.