Reason tank DPS stat was changed to STR

[Jandor]

The new weakness penalty imposed by dying is -25%/-50% to STR/DEX/MND/INT. This limits damage dealt and HP healed, while keeping HP and MP values intact (previously was a 30% penalty to both, which made surviving mechanics after raising from a death, exceedingly hard). Since the new changes, tanks' damage is calculated with STR in mind, so that when tanks die, they incur the same damage penalty as DPS jobs do.

I don't think tanks were changed over to STR because of the changes to weakness. I think it was changed because VIT is the only main stat that affects something other than damage, namely your max HP. Scaling tank damage on VIT makes it harder to tweak tank HP/tank DPS independently of each other.