Here's some relevant information on tenacity for those that think it "scales terribly"

And something a user pointed out: "People just need to look at these lines together.
Determination gives 1% bonus damage for every 170 points
Tenacity is still inconclusive, giving estimates between 180 to 220 per 1% bonus damage.
Tenacity is estimated to be not that far from Determination, and Determination is generally seen in a neutral to slightly positive light right now."

It requires slightly more points than determination to be an equal damage increase, but ALSO decreases the damage you take. And then comparing it to Direct Hit...
"Correct me if I'm wrong here, but assuming 39.09 rating per 1% chance to DH, and 190 rating per 1% tenacity (midpoint of where the post said it would be), 18 slots at 40 rating per slot (current gear).
40*18=720 rating
720/39.09*.25=~4.6% damage from direct hit.
720/190=~3.79% damage and 3.79% damage reduction?
So if we, for arguments sake, say that a tank puts DH in every slot, or tenacity in every slot, they would give up ~0.8% damage for 3.8% damage reduction?"