Not so unbalanced bear tank on Thorim?

I have been thinking a bit today, and I hope that some of my readers that are more into theorycrafting than me could correct me on this one…

I was thinking about Thorim’s Unbalancing Strike ability, which reduces the defense skill of the affected target by 200, making them crittable.
At first I was thinking about how high his crit chance would become when the tank got that debuff, and, if the math is the same as with defense above 400, this is what I calculated:

According to wowwiki, 1 point of defense skill reduces the chance to be critically hit by 0.04%, so
200*0.04%=8%

What now if the tank somehow manages to overcome that 8% gap?
(This mainly applies to druids, I don’t think the other 3 tanking classes would have any chance of gaining an additional 984 defense rating)
For druids, we must somehow get 7.6% less chance to be crit, which is basically 623.2 resilience rating, and that should be fairly easy when thinking that our 3.1 BiS tanking gear might probably be the S6 stuff.
Basically, I was thinking that it might be possible to tank Thorim with just one tank without having to rely on taunting the boss, which would allow the other tanks to do a bit more damage (switching forms, stances, or presence) and therefore beating him more easily.

I came upon this idea after thinking that a feral druid might use glyphed Barkskin to survive being hit by the Unbalancing Strike, but unfortunately I wasn’t able to find any information on the cooldown of that ability, so barkskin might not be ready every time one might need it…

Comments and corrections are appreciated.