smbakeresq
Explorer
They can also be useful for classes which might be able to get bonus damage based on elemental affinities. Draconic Sorcerer, Celestial Warlock, and so on.
Except that the enemy can choose to stop at any time, including after being hit by the OA, and thus not take the damage. This could backfire if you're a class which doesn't necessarily want the enemy to stop and do a full attack in front of you. Just something to be aware of.
Correct. Most DMs won’t take an OA unless they are forced into it through something, they will play enemies far smarter and with total knowledge of the PC abilities then the creature would be.