Personally, I think Vergil already unlocked "Angel Trigger" because his DT looked Angelic when compared to Dante's.
It was a form of contrasts; Dante looks demonic but has a good soul, while Vergil looks angelic but is rather self-entitled.
They had concept art made for Dante's Angel Trigger, but design was scrapped and given to Vergil. Now Vergil is permanently stuck in Angel Trigger -- a reference to the godlike Mundus boss from DMC1 in my point of view.