I think each class needs it's own ultimate ability that would provide player with unique tanking experience and. But the problem is some classes just don't have one or even if have one, it is not helpful or reliable so no onen uses it.

For example, I always liked Magma Armor, but the shield effect from it has so small radius, so no one uses it (me also: i tried, but it's so difficult to utilize) and prefers something like Shield Barrier (even though it scales with offensive stats, it is still more reliable on a tank than Magma Armor).

Wardens Permafrost, I assume, is supposed to be tank ultimate. But no one uses it because its bonuses won't save you or your teammates in tough situation. So maybe add bigger shield on targets hit at cast and lesser shield stacking on them every second that they are standing within the range? Or maybe add new defensive buff purely for PvE that would give bigger numbers of damage reduction (like 30% Major Protection had in the past). We already have offensive bonus unique to PvE (Empower), so why not to have defensive one? Yes, we have Aegis, but its numbers are small, it is permament and only obtained with armor sets.

Veil of Blades is also not used by anyone. If it had bigger radius, it's cool synergy would be more reliable. Seriously, I have almost not seen someone using this synergy. And Major Protection with its 10% damage reduction is far cry from emergency button in PvE. It could also add blind effect on enemies (fits skill's theme).

Some classes don't even have tank ultimate.

Some of those ultimates could taunt all enemies around (don't know which one is better).