Also, bear in mind that the above discussion applies to collaborative tanking scenarios where MT and OT are working together to maximize raid dps. It doesn't really apply to situations in which two tanks are spamming their RoH, BB, or PS combos to determine who is truly more metal.

Just doing some napkin math, the BB combo does about 797 enmity potency per hit and SE does 203 (alternating between the two averages to 500). On DA SE is about 267, Del is 226 and PS is 857. Even when you factor in Grit, DA SE becomes 614 and Del becomes 519 before accounting for the damage reduction modifier. If you're both trying to maximize your respective dps, it can be tight at times, and there are going to be moments when one of you will have to make a compromise.

Enmity is always the tank's responsibility. But even though we sometimes view OT as a form of specialized dps class, it still is a tank, and its actions (even ones used to maximize dps) have inbuilt enmity modifiers that can rival (if not exceed) the enmity of being in tank stance. Accidentally taking enmity as OT is like messing up a tank swap. It's an error, not a sign of exceptional dps.