Turn 5 Downed by JP Group? Exploits or Legit?

[Eronn]

You're not getting an extra 5% mitigation from 30 STR.

Based on my understanding of the tier system, this is correct. 30 STR will allow your Blocks to block for ~1% more and Parry to parry for ~1% more, assuming those points push you over a tier. If they do not push you in to the next tier then they are giving you 0 mitigation. It all depends how close to a tier you are, but in general it is not worth it.

As to the 5.8k, it is highly unlikely you are going to be surviving the later phases of Turn 5 with that little base HP, assuming you are MTing. I have that being our off-tank and I am frequently within a sliver of being one-shot through cooldowns.