You didn't read the essay I wrote a few pages ago, did you?
As killing the boss is a goal of the group challenging the encounter, anything a tank can do to contribute to that is worthwhile, and part of their job. Yes, a tank's first tasks are holding aggro and surviving, but those are comparatively easy in this game (I remember being encouraged when I started playing that the challenge in tanking gameplay would come in managing enmity; 40 levels later, I now know the truth). You survive the tankbuster, and you mitigate enough damage passively so a single unbuffed Regen can keep you up. What do you do?
You do damage.
If this were any other game, if surviving and holding hate required more effort, then maybe you could say that damage output is not in the tank's job description. But this is FFXIV. Encounters are easy to survive, and tanks are given tools where they can increase their damage without really sacrificing too much mitigation or enmity control.
You seem quite bitter on this. I've actually had healers thank me for using Clemency and Stoneskin when the fan starts getting poopy, as there can be situations in the game that require a lot from healers (yes, mechanics are easy, but some people, man...). Advice on the forums almost always revolves around the current Savage raid, and how to operate in a PUG.
But everything you read on here should be taken with a grain of salt. People give their opinions and often clash about them - that's exactly what's happening in this thread. Yes it's usually a good idea to try to maximize your damage output, but there may be situations where a well-placed Clemency or Stoneskin can save a healer or a DPS from dying; how much group damage did you contribute, then, by keeping that person alive?
The key is communication. If there's a part of the fight where you know healers are struggling, ask if they want you to throw out a Clemency or a couple Stoneskins (which, by the way, are a great alternative to helping mitigate group damage without contributing to overhealing). If they don't want it? Focus on surviving and on your own damage - at least you asked.
Except they are. See point 1 for more info.
If you think tanking in FFXIV is so boring, why tank?
Damage output has always been a part of tank gameplay, as the fallback when you don't have to focus on enmity or survival. FFXIV downplays those, and so gives tanks more opportunity to "live dangerously" and maximize their output.
But as I keep saying, at the end of the day, if you and your group meet success at an encounter and you all have fun, then your damage output and effective mitigation are completely fine. Guides and forummites will tell you how to maximize your damage output, but in reality that's just because survival and enmity are pretty straightforward in this game, and because doing more DPS is never a bad thing.
EDIT: Just realized that if you'd told me six months ago that I'd be on this side of this discussion, I'd have called you a liar.