Intuitive Tanking.

[Anova]

My first point is that enmity is rather a simple thing to handle and achieve. It's not hard nor interesting (especially for paladins).

It sounds like you just have burnout from playing a tank. I'd really just take a good long rest from it if possible.

My second is that as your gear increases, endgame bosses become trivial in damage done to you.

That is to be expected. You will obviously do better in i100 gear than i55. That's the whole point of endgame gearing and players will be able to push themselves further. On that thought, there's a frontier for tank dps I think is viable, similar to white mage and cleric stance. May I suggest you try experimenting switching between shield and sword oath in those easy fights? I'd really like to see that catch on but my own PLD is still too low level to push it. As an alternative, I know I'm not the only one who spiritbinds in dungeons. You may consider exchanging some of your equipment for spiritbinds on the easier runs to maintain the difficulty level and earn some extra money/materia you need.

My third is that since fights are being solo tanked, it reduces the desire for two tanks in a group, which is a bad thing for the tank population, as they are less needed and therefore more likely to roll something else.

If anything, I think this is a sign there aren't enough tanks, so players are coming up with ways to use a single-tank to gather partyfinder groups faster. It doesn't help that for most 1-tank parties, everyone is massively overgeared for the content. Just consider it as an option only for elite tanks (not every tank can do it).

Here's what I suggest: Battle Fatigue. A mechanic that slowly causes you to take more and more damage the longer you tank something, and increases based on the rate of damage you take. Doesn't have to be a huge amount, but enough to cause you to control or think up of creative ways to reduce the amount of damage you are taking.

And then while you are not tanking, you recover from the battle fatigue, perhaps stacking even higher defense proportional to how long you have not been being railed on by the boss.

Several bosses in endgame already employ a similar dynamic. I would ask you to mind the learning curve and ask that you don't require it of fights short of Extreme and Coil. I know you're bored grinding dungeons for myth, but HM dungeons are designed for players below or at i90. I can see the new dungeons benefiting from it however (since they're approaching ADS level on the new HM). Stone Vigil HM and Hullbreaker have several examples of a boss that can't be tanked or escalating damage mechanics that SE is playing with. I wouldn't call them a resounding success, but they are in development. I don't know what more you can ask of them.