Congrats on your spell where your spellcasting roll has literally no effect at all and it does absurd amounts of damage and is almost entirely unblockable, thus making it superior to every other possible option else in the game?
The number of hits not mattering is odd, but this is certainly not the only place where that's the case. Detox is a "did you get a hit" spell.
As for absurd amounts of damage - I think we'll have to agree to disagree here. Since it's a Force-dependent spell for damage, you can't pull the old Force 1 + Reagents/Edge trick to get decent damage - you have to cast it at Force 6 to get 6 damage. Which means, to get an "absurdly high damage" you practically need to overcast it, which means more drain.
Secondly, it's not really absurd because you end up needing to do more to do the damage. Unlike a spell, which requires good Magic and good Spellcasting, good Willpower and good Drain Attribute, you now need some Magic, some Spellcasting, good Willpower, good Drain Attribute, good Agility, and good Clubs/Blades. Remember, they can't dodge a Stunbolt, but they can dodge a Manablade. You have to invest a lot more to make it good.
Thirdly, since you can't use the Low Force + Reagents trick, you'll need a good sustaining focus or you'll be pulling sustaining penalties as well.
I think it's a stylistic spell with upsides and downsides. Until I see it in play, I can't judge whether it's balanced or not.