2 Target Rotations and their problems.

[PyurBlue]

You don't AoE with two targets you do your single target rotation minus I guess dots on two targets if you want to be fancy.
It's not really a problem it's intended.
The potency is designed so that you should do it with 3+ targets.

Two target rotations are, or were, very much a thing and add some depth to DPS rotations. On BLM you replace Despair with Swift Flare, two casts of T3 per rotation, and replace Xenoglossy with Foul, which mixes things up a bit. The reason why this is rarely used is because having just two targets is pretty rare.