The big reason why stacking Strength on a Tank is possible is because the difficulty of this game is much, much more in the mechanics than it is in the numbers. Even when a piece of content is given a Tank at the minimum iLvl for it, monsters are still doing far less damage than their target's HP pool would suggest that they can handle. So many bosses are of the "Tank Buster! auto auto auto Tank Buster!" pattern that healing isn't about HPS; it's about skillfully getting Stoneskin/Adlo/Tank Cooldown up to take the buster, heal the tank to full, and wait for the next one.
So, the devs really should decide which path they wish to take with Tank gear: lower HP gains to better match incoming damage or make everything hit harder to actually require the use of Fending gear. This tier has been unbelievably egregious with a Tank's ability to complete the hardest content without increasing their maximum HP by even a single point over what full i110 VIT would give them. You know something a bit funny when it's everyone else who needs more HP, not the Tanks...
