But that isn't how things are in FFXIV. In FFXIV, the so called DPS deal a mere 20-30% more damage than Tanks and Healers. Bards and Machinists have been called obsolete because Tanks are so close to their DPS
Let's talk individual stats in Final Fantasy XIV
I think starting to see what is possibly the largest flaw in the design of this game. We have here a game that features the Holy Trinity of Tank, Heal, and DPS... but is absolutely abysmal at enforcing it.
Ordinarily, there are the three roles. First is the DPS who specializes at dealing damage at the expense of a limited ability to take hits and support the party with buffs/heals. Second is the Healer who specializes in supporting the party with buffs and heals at the expense of limited ability to deal damage and take hits. Finally, we have the Tank who specializes in taking hits at the expense of limited ability to deal damage and support the party. Put all three of these together and we get the Holy Trinity because the three most major aspects of a party's ability to fight an enemy are covered. The weaknesses of the individual roles didn't matter; they were all so necessary because of what they specialized in that all of them were always needed, and therefore they were always there.
But that isn't how things are in FFXIV. In FFXIV, the so called DPS deal a mere 20-30% more damage than Tanks and Healers. Bards and Machinists have been called obsolete because Tanks are so close to their DPS. There are fewer than five fights in all of Heavensward that couldn't be easily cleared without bringing a single DPS along. Tanks can eschew a majority of their ability to take hits and still tank an encounter. A healer can spend less than half of an encounter casting healing spells and still easily keep everyone alive. Eliminating Tanks and Healers from encounters is always at the forefront of player's minds because the number of them that the game recommends for parties is almost never necessary. That's the big theme here: there are too many party based situations where one or more roles simply aren't necessary.
So... Tanks. As i have observed, they are currently caught in a fallacy. They're being told that they can only be effective Tanks if they stop thinking like a Tank. Healers are in a similar conundrum. The driving reason behind this, I would guess, is that the community is increasingly valuing DPS above all other factors in determining the effectiveness of a party. This is because of the way FFXIV handles difficulty. The primary difficulty of most fights is the handling of mechanics. The rest of it is the numerical difficulty: the amount of DPS, healing, and mitigation necessary to survive and win. The only truly significant element of numerical difficulty fights in FFXIV tend to get is a DPS check. Hard checks on Healing and Tanking are much rarer and are frequently only valid when a group is undergeared for a piece of content or players are otherwise deliberately doing something to increase the difficulty of a fight.
So we have DPS checks in every meaningful fight, a DPS role that doesn't deal that much more damage than the other roles, and Tanks/Healers who have absurdly easy access to ways of increasing their own damage without removing the ability to perform the minimum of their own assigned roles. Of course DPS is going to be the stick by which everything is measured. Thus, the Holy Trinity is abolished. Instead of Tank, Heal, and DPS... we have a DPS who can take a hit, a DPS who can heal a hit, and a DPS who hits a little harder than the others.
There are two questions left here. First is whether or not this is actually a huge problem, in the sense of some perceived ability to kill the game. The game has been running strong with these design philosophies for well over a year now. If this skewed trinity were to kill the game, it probably would have succeeded by now. Granted, it probably has lost subscribers in people like you who looked at a non-DPS role and realized that it's just a DPS that happens to have a specific utility, but it seems evident enough that the community at large is having fun with the game as it currently is. If you wish to Tank or Heal, it might be truly necessary to leave behind what those roles fully do in other games because it just doesn't apply to FFXIV right now.
The second question is whether or not SE might ever consider changing the game to make the roles more defined and necessary. My best guess is that they probably won't. One thing they have been particularly loathe of doing is making changes that significantly muck with established player strategies or practices. Strength Tanking has been happening for a very long time now and they publicly acknowledged DPSing healers shortly before Heavensward came out. Square Enix knows that this is happening and it thus could stand to be reasoned that they're deliberately enabling it to occur.
This situation is rooted down well enough that a mere increase in the amount and/or effectiveness of defensive stats for Tanks will not do a single thing to change the landscape. All it will do is piss people off because there are now more defensive stats to avoid.