Well, nobody says you have to take it.
But Storm Of Punches compares very favourably to Blaze Away and Wall Of Death (which are both canonical), so I'm not inclined to buff it.
I suspect that your issue may have more to do with your problems with Fists as a skill than with this stunt.
How balanced would you consider a stunt that gave Athletics' dodge trapping to, say, Scholarship to be? Or Resources?
Would you rate that stunt's power on par with Footwork?
Or would you analyze the power of the stunt within the context of the skill it applies to?
Both Weapons and Guns attacks almost always have a weapons rating (only even
effectively not having a weapons rating when the target's armour meets or exceeds the actual weapons rating, or when dealing with 'special attacks' like tazers).
Fists attacks default to having a weapon rating of 0.
Spray attacks rely even more heavily on weapon rating to inflict stress than do normal attacks.
Spray attacks made with Fists, then, are, by default, less powerful than those made with Weapons or Guns, even more so than is true for non-spray attacks.
As such, a stunt granting spray attacks is less valuable for fists than it would be for weapons or guns.