The whole point of a tank is to keep the mobs attention. So, the next logical question that follows is, how do you mitigate damage, so the tank is effective and doesn't die.
If the whole point of a tank is to keep the mobs attention, why are you focusing so much on how a tank mitigates?
The reality is, a tank has two primary jobs: surviving incoming damage, and holding the mob's attention.
While individual games vary, it is typically common that a tank has done all they can for their survivability once they begin a fight, and most of what they do during the fight is with relation to holding the mob's attention.
There is a nearly infinite varieties of game mechanics that can be implemented to make this appeal to different players. Maybe someone wants to hold hate by healing themselves. Maybe someone else wants to hold hate by smacking the guy with their sword. Maybe someone wants to hold hate by throwing fireballs.
There is absolutely no reason there can not be a variety to tanking classes, much the same way as there is a variety to damage dealing classes.
I'm not even going to bother with you anymore, you sound like the radical environmentalists who want us to go back to living like the days of our ancestors, the point being you don't know how to comprehend the reality of the situation, and when I try to explain it, you say 'Nyuh-Nyuh-Nyuh'.
I'll take the bite though one last time, let's see if you can understand this.
It doesn't matter how much you can mitigate, if you can't keep the mobs attention focused on you. If you can't do that all else becomes moot. Your abilities are rendered useless, your purpose is rendered useless. Keeping the focus of the mob on you, is the main priority. Once you know that, then you can ask, how can you keep the tank alive?
There again, the only two survivable mechanics, are either taking damage by absorbing it through HP and healing it back (Whatever the amount, whether it is 500, or 50, doesn't matter its the same mechanic: You take damage and heal it, if you don't heal, you die.), or you negate damage through avoidance. Period. There is no other mechanic. It defies all logic to have another mechanic. There simply, is no other. Every other thing you proposed is a variation of the two mechanics.
Now, instead of watering down those mechanics between many jobs, you can instead focus on the two mechanics, in two jobs. One avoidance, one blood tank. Instead of taking their abilities and moving them across a wide range of jobs essentially, creating clones and watering down each job, you can instead keep them on one job, flush it out, make it exciting, fun, active skill based and entice people to either avoidance, or blood tanking and you can differentiate skill styles within those jobs. There is no reason to have more than 2 tank jobs.
Your rut, is you think you need a new job for every different variation of the only two mechanics that tanks can utilize. I explained why this is flawed thinking and how it actually hinders people wanting to tank. So you have 2 tanks, each mitigating damage the same, but different enmity mechanics? So, essentially, it is the same job, what makes you think people are going to want to play those jobs since they will be taking abilities from each other.....watering them down.
I hope SE learns from their mistakes and creates no more than 12 classes at most for FFXIV throughout its lifetime. I'm tired of jobs being clones of each other. Jobs need to be different from each other, that creates diversity, it also allows for jobs to fully function their roles without several overlaps. It also makes balancing much easier, and it also makes expanding those jobs in the future much easier. Once you get 20+ jobs you start to create gimmicky duplicates when you have to find ways to expand the jobs in content upgrades and patches.
Anyways, I'm done after this. There's no point to argue with someone further who is entrenched with their dogma.