The point in your TL;DR was what I was using all of that to really convey.

On the topic of secondary stats themselves, though, I believe secondary stats to not matter at all in the sense that there is no combination of stats that will literally prevent you from being able to complete a piece of content except for too little accuracy or too much wasted accuracy. Going by Role:

Healer: Secondary Stats literally don't matter one iota. Choose your favorite and have fun.
DPS: The difference between the "least optimal" build and the "most optimal" build is a difference of less than 0.02% in overall potential DPS. The only consideration that needs to be made is not to let Speed get too high in relation to long fights.
Tanks: They only slightly matter here for damage, because Tanks have the ability to switch damage increasing secondaries for Parry. I'd figure that you could eke out an extra 4-5% overall DPS at maximum if you switched all Parry for all Damage. An extra 4-5% on low damage which is further reduced by Tank stances.

If you want to increase Tank damage, stack more STR. That's the only way it'll be worth anything noticeable.