I find that a second Shadow Flare during the AoE rotation shouldn't need to come until after the second tri-disaster that comes after the second Bane, assuming you didn't waste any time at all in the meantime.

And I always spam Tri-Disaster if there will be 3 or more targets left alive by the time it resolves.

I also never have AoE aggro issues, that is most likely a fault of your tanks. Even the BLM going balls out with multiple Flares doesn't seem to pull aggro.