Never, ever, factor in DPS when tanking as PLD. The damage increase from +STR is still going to be negligible because you should be using Shield Oath in most situations and you're already losing 20% outgoing damage with that. The block rate returns from +DEX are negligible, so the question that remains is:

Is the amount of extra damage you block while having +STR equal to or greater than the amount of HP you gain from +VIT over the same time period?

If +VIT gives you, say, 500 additional HP, then the additional amount of damage your +STR build must block is 500 damage in the same time frame you would lose it in a +VIT build, assuming consistent healing.