What I'm seeing is a buff to vit tanks, and a nerf to str tanks. I'm not seeing this as a buff to tanks in general.
There was pretty much no reason to wear vit before this patch once you had a certain amount of defense. Now gearing for vit will give some additional bonus, at the expense of str not being as useful. I wish I had the numbers to know how much, but all that I know is that vit tanks will now do some more damage, and str tanks will now do less damage.
Maybe str tanks will still do more damage than vit tanks. But no matter what, I'll be weaker than I am this patch. I can only hope that the damage weight of vit is high enough that I won't miss str tanking all that much.