Kael 6* can farm brutal 12-3 by himself if built with lifesteal. I used him for a while and he did it easily, but He did have all the way through tier 3-4 masteries.
As far as best? No I think that title goes to Queen Eva. I have her maxed and full masteries and she farms 12-3 in 7 seconds.
Foli is ranked number 2 in Arena as Best AOE Damage Dealer.
It is because Foli AOE can block revive people.
Foli was my very first champion as well.
Foli is amazing.