I have a new theory now.
With a Roar Animation, broken damage scaling allowing it to one shot players, and a need for clash visuals, I think Surge is a Continuous Fire Beam.
Think a Kamehameha, a beam that you fire nonstop for a few seconds thats meant to stack damage. Got no proof, but it would make sense. The only times damage breaks hard enough to kill people in one shot is on multihit spells. Surge as a name could fit this still, a ‘surge’ of magic in a continuous line. Then a roar animation could be something in line with Broly roaring his beam in Dragon Ball.