Honestly I feel like they should just remove the damage+ component and buff the damage mitigation component.
Sure, people will still push for damage+ 95% of the time, but at least it would have a bigger per-point impact. The current hybrid effect that it gives is awkward, which further makes it more useless.
One of the biggest issues with Parry was that it did nothing for magic damage.
Furthermore, bosses didn't hit hard enough to need to spec toward mitigating damage and cooldowns were/are the key way to mitigate damage.
This area actually touches on the "issue" of tanks wearing STR accessories at the moment - because you only need enough HP to survive. A bigger container doesn't actually make you take less damage - it just gives an inattentive healer more time to react.
If their goal is to confuse players with these strange substats, then they are doing a good job of that. I thought their goal was the exact opposite?
I am personally of the opinion that we need MORE substats that allow for wider levels of customization, even if this customization is an illusion (as there will always be an "optimal" BiS build).
I like the idea of tanks having the ability to jump into a DPS gearset for easier content, or switch to a damage mitigation / HP set for harder content or raids, however you could blame the current game design on this but there is no need for this - and DPS is the next best option.
So I am of the opinion that removing the damage+ side of Tenacity and focusing on the mitigation side would be a step in the right direction for this game.
It would not only "simplify" these stats for people that don't like to aim toward BiS, but it would apply a big enough per-point effect on an area of stats that we currently lack - mitigation.
The ability to actually have a stat to manage how much damage you take - and one that actually works to good effect, would be largely beneficial to the masses who find it difficult to heal a tank in some content in the game. On the flip side of this, it wouldn't stop the more skilled players from maximizing their ability to deal damage by pushing for higher damage stats.
More horizontal gearing options is something I absolutely encourage.
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As for the META argument...
95% of the playerbase shouldn't even worry too much about it. The meta is really for the 5% that push speed runs, world firsts, etc etc.
Playing optimally should definitely be encouraged, however if sacrificing damage for survivability helps your group clear content, then you should do that.
The meta is for players who are able to execute their job roles flawlessly or at least to a high level. Most groups don't do that. So the idea of forcing yourself into a meta of certain jobs / BiS options, is actually going to limit your success.
Groups run into problems when they focus too hard on playing around the meta of the 5%ers. Just stick to the stuff you know, and what works for your group. If that means stacking mitigation over damage as a main tank, then so be it.
(Though currently, Tenacity is just rubbish..)