Tanks in raids are, for the most part, completely useless. I'll break it down:

Healers: a healer's job is to heal folks. If your group is good to go, you you have visibility into the other groups and can heal those folks, too. Due to generally constant damage being applied by the enemies, you're almost always doing something. If you die, people usually get you up ASAP because the easiest path to wiping is all dead healers.

DPS: hitting crap is your job. You are always doing your job. You're not expected to heal or take hits but it's great if you have the ability to do so. To be honest, if I'm healing a raid - unless tankbusters are involved - I tend to revive the DPS before the tank if both are down.

Tanks: your job is to take damage that otherwise would have went to the raid. Here lies the problem.

Other than the trash pulls, most raid fights consist of one creature that does all of the damage. One creature. Three tanks. That means you have two tanks doing subpar damage pressing the 3 buttons from their main rotation and the occasional damage cooldown. All those damage mitigation buttons and other tanking skills go unused. The only time you feel "important" is when the critter throws out "tankbuster" attacks. Big whoop.

I suspect this is why I see so many tanks provoking off each other or tanks who think they have to tank the entire instance. It's outright boring to go into a raid instance as a tank and all you get to do is be a lackluster DPS.

What can be done to fix it? Well, this will require SquareEnix to do something more substantive than "oh, we'll throw in a tankbuster" in their raids. Tankbuster attacks are the laziest way to add an artificial need for an otherwise unneeded tank. Another thing they've tried is adding trash adds to the fight, but those phases are maybe 5% of the entire fight. It seems like they'll either need to completely rethink how they design raids, put some kind of lottery system into bosses, or they will have to do something like remove tanks provoking and require tanks shirking; none of these sound appealing in the long run. Alternatively, it tanks could just rotate through the bosses. But this would require the entire tanking community to change this mindset that they have to tank everything - something I'm equally sure will never happen.