There's also the normal attack cap!
... but it's ridiculously high, 350k per attack (so 1050k on a triple attack). This is a number that is hard to reach even for the most dedicated of whales.
Basically only possible to reach with the Stun damage+ skills, having crazy high base attack and stacking attack/elemental buffs like crazy.As far as I know, there's no cap.
However, notice that atk buffs are literally Assault. So if you have 120% Assault already and give Azazel 120% buff, Azazel will have 240% Assault. Or 340% in Union content.
Numbers like that do wonders if you can put some additional modifiers into the mix, like Berserk.