The bow ultimate Ballista deals X physical damage over Y seconds, literally "damage over time." However, it is being treated as "direct damage" by the game, as it scales with Master-At-Arms CP not Thaumaturge CP, and is unaffected by DoT buffs like Necro Rapid Rot passive or the 5pc bonus on Deadly set. I've submitted a ticket in game, but haven't tested the base ability or the other morph.
PC/NA || CP/Cyro || RIP soft caps