I swap adds and boss with my partner on Horridon and can easily survive the triple combo. You should use barkskin for every direcall anyway, and with T&C + Savage Defense, the damage is pretty negligible. During enrage, the rotation of cooldowns, your own and external, and bops if you are lucky enough to have them, make this a breeze.
I tank the bats on Tortos, all you need to do is put on a few bits of stam (trinket, maybe some gems), and this fight becomes a joke.
Heroic Sha, we never killed, but we did have quite a few attempts into the final phase, and I always tanked the boss, while my cotank took the naked and afraids. Our wipes were never due to me dying.
I don't really understand your logic o.O I have maintanked every fight this expansion so far.