Red Mage as possible new tank class

[Duelle]

I can't speculate on whether or not this was the original intention of Ninjas in 11, but after 10 years of it working that way, it's pretty apparent that they are fine with it.

The only reason it was left alone was because it took over the rest of the game. It would have taken them more work to fix defense and make NIN not mandatory for content that was even remotely challenging.

And just because they aren't blocking an attack with a shield does not mean they are any less capable of being a "tank".

Who said anything about blocking attacks with shields? By that logic I should oppose WAR tanking due to them using a two-handed axe, when I wholeheartedly support their cause and existence.

Here's five tanks, all of which mitigate damage rather than entirely avoid it:
Sword & Board tank with a slight advantage on single-target
Sword & board tank with a slight advantage in AoE
Two-handed tank with self-heals and active mitigation via a damage shield
One-handed tank with high armor, tons of HP and some dodge
Two-handed tank with procced parry increases and splits incoming damage into two - part instant, part DoT (this might be a good foundation for SAM if we were to want it as a tank)

Here's one I proposed:
Rapier-wielding tank focused on parrying and dodging with active mitigation through damage shields by spending their gant (yes, Mystic Knight)

There's probably more than can be deviced without having to turn to a mechanic that causes more trouble than it's worth.