Imperfected
Member
I think ENB hinted that the Tonitrus had some hidden(?) bonus arcane scaling on one of its attacks as well.
He probably just means the "charge-up" feature that gives it 7 seconds or so of increased damage. The stats shown in the equip screen don't take it into account, and it's a major contribution to the damage of the weapon.
I don't think any of the actual attacks have very large multipliers, since it has such a limited moveset, but I could be wrong. Damage multipliers on moves is definitely something the community's sleeping on, as it's a major factor in how good a weapon actually is versus how good it is on paper.