I refuse to believe that your response to 'tanks can run out of cooldowns sometimes if they space them badly or the overall DPS of the party is very bad' is to remove literally all the defensively oriented nuance that the entire game has, or that your idea of 'rewarding good gameplay' somehow involves removing all of the actual gameplay?

Using single target combos to keep up a defensive buff also runs counter to trying to keep aggro on multiple mobs, and I can't imagine an idea worse than 'well the DPS should just hit the thing that the tank is hitting' because... why would you do that? In this situation, who's actually having fun? Certainly not the tank who's losing aggro due to bad job design, nor the DPS who are dying because they're trying to AoE, nor the healer who can't keep up trying to heal the entire party based on which DPS has aggro on which mobs.

It doesn't even work as it does for physical DPS because all of them aside from Dragoon have passive upkeep on their buffs via their AoEs now. Ninja upkeeps Huton via AoE. Samurai upkeeps the haste and damage buffs via its two step combo. Monk, which previously did in fact accrue greased lightning via AoE prior to the removal of greased lightning stacks, still extends Twin Snakes via AoE.

Hell, Warrior, an *actual tank,* also upkeeps Storm's Eye via their normal combo, and that's the better consideration to make anyway because doing a single target combo to get the buff *while* you're trying to hold aggro on multiple mobs *and* pull to the next pack suuucks.

I am genuinely not going to even attempt to touch upon how much this obliterates the concept of playing tank defensively in any content that's not a trash pull in a dungeon.