I have found Bane & Fester to useless at 50th lv, what I found very useful is Energy Drain as a Cannon. It is 150 Potency, with the Restores MP ability. I have also put into Macros (Bio; Miasma; Bio II) This is because Bio is a mobile spell. This way I'm only stuck in 1 place for 5 seconds. My roll changes by the needs of the party.
Don't call Titan Egi a Tank; it is a heavy AOE dealer. You may say its only 70 Potency every 15 seconds, But it is adding 70 Potency plus holding all adds in a 5y area, which is important do to 2 of your 4 AOE's are zero range (Miasma II & blizzard II),
while Bane may seem to be an AOE, it only targets a randomly +3 targets. In a party with a large pull I spam the Tri-Disaster, It maybe only 30 potency, but in support of Titans & the parties AOE's it dose plenty damage. Just remember to use Energy Drain to minimize MG loss. While Virus cool down is bad, I use macros; Ruose and Spur and Virus, to make Virus useable.