In my experience Ffxiv is a very very easy game on most parts. It's true, in "normal" content, as a dungeon run, heal dps is a nice to have, but in no ways required. If our healer contributes to dps while keeping everyone alive, I give him my comm for playing his class better than average players I meet. If he doesn't, I don't care and the run just takes a little longer, no biggie.
It's a different story in savage Alexander and extreme primal
Here I consider healer dps as a boon to the party, that can't and shouldn't be neglected. It makes the fights not only faster, but is the little bit of additional power that makes the party skip mechanics or even win the fight. But people who run that kind of content seriously usually tend to do their best at maximising their performance, so healers in there usually do dps whenever their time and mp allow it.