Ideas for a Caster Tank

[RitsukoSonoda]

Please explain how this tank will then tank enemies that are immune to magic damage, or reflect magic damage. That is the single biggest flaw in the notion of a purely magic damage dealing tank.

Tanks should ideally do the same kind of damage as each other because having one that does a primarily different type of damage opens up major balancing issues. You'll end up creating a tank that either no one will want in their parties, or only want in their parties. By keeping them all slashing damage it eliminates a factor they'd have to consider and balance.

I don't immediately recall any enemies that are specifically immune to magic outside of a possible temporary buff as this would make all caster DPS useless on the enemy as well. As for reflecting damage there are enemies that use effects to reflect physical damage already so reflecting magic is moot. FFXIV doesn't even appear to really stress elemental resistances either as a BLM can kill a fire elemental with fire as easily as just about anything else in the game.

As for supposed "balancing issues" with a tank primarily dealing a different type of damage than the 3 current options.
WAR, NIN, SAM can all inflict slashing resistance debuffs.
DRG can inflict a piercing resistance debuff.
MNK can inflict a blunt resistance debuff
BRD can inflict a magic resistance debuff

Now granted much like elemental resistances overall damage type resistances aren't extremely prominent either in this game unlike FFXI where there was an easily noticeable difference in base damage with a lance when used on a colibri and a skeleton of the same level.

Damage and element types in FFXIV play no where near as big a role as they did in other FF titles. The most that is going to happen by offering tanks that don't primarily rely on slashing damage is make the theory crafters think harder about how to min/max a party comp to come up with something that will only be used on savage mode and the supposed super savage that is coming.