HP and Damage Mitigation are only two of the three concerns for a tank. The third concern is Threat Management. I don't know how many times I yanked off of a full vit tank with a STR PLD in SwO (this was pre 3.0). If you're making your dps hold back or they are yanking off of you, HP and Damage Mitigation are irrelevant. Yes there is a balance but to say to go one way or the other is just silly.

But I agree that fending gear needs a mix of VIT and STR.