Was in Titan Extreme today and a healer went down, so being the off tank I used cover on the main tank to help spread out the damage while the resurrected healer recovered. I didn't realize in the hectic battle at first, but I had a stack of Mountain Buster on me. Huh? I know I didn't get hit by it. Meanwhile the main tank was able to tank all the way to post heart phase without a tank swap, because my mountain buster stack meant he didn't get his.

Not only does this mean less damage for the healers to heal on the main tank, but it simplifies the tank swaps if it's the same tank all the way until gaolers are dead.

I later confirmed it works like this by joining duty finder and testing.

Now I'm curious where else it works like this...