First, I didn't talk about TA and HC value in raid. These are very strong and valuable.
I said that saying "NIN threat generation will increase Tank dps significantly" is a bit far fetched. And this was making some gruesome assumption such as "1 dps combo does 50% more damage 1 threat combo"which is not true
Just to take DRK (the tank i'm the most familiar with)
Threat combo does 670 potency
DPS combo does 700 potency (536 effective potency with Grit, -20% damage)
The dps combo then deals 30% more damage.
You can argue about min maxing the Dark Art and mana gained from the dps combo vs threat combo, AA etc but I doubt this will result in the threat combo (under grit) effectively dealing 50% less damage than the dps combo.
This was also considering a fight with 6min of effective GCD on the boss. The longer the fight, smaller the gain will be.
My point was NIN threat management is a strong tool in threat management, not in raid dps gain. (spare nich situation)
Increasing the tank dps by, at best, 2% is NOT a significant raid dps increase. It can be a useful dps gain on an add (OS3 for instance), but over the course of a fight the damage gain will be trivial. Therefor, NIN threat generation tool should be balanced around its usefulness and not the trivial damage it brings to the raid because 0.15~0.2% raid dps is not a significant it is a dps gain, but it is not significant.
Your raid dps will vary more from your AST card draw or how many more crit your SCH libra allowed to land. (sometime it's 0, sometime it's all attack)
If you fail a boss and wipe from enrage at 0.1%, the cause will most likely not be "our tank didnt do 300 more potency, nothing else could have been done to compensate our tank 3 GCD damage loss from its threat combo".
There will be a long list of minor things that happened throughout the fight, the eventual dps gained from NIN threat skill could be added to the list, but a dps dying once, failing one GCD, your healer missing a few DoT uptime, etc etc etc, abad crit streak from a single dps, even poor card draw (chain aoe spire/ewer).
This will have a significant impact on the raid dps.
That's it, so NIN threat tool on tank pull it is a dps gain, but it is a trivial dps gain and should be considered as such.