Hello! Thanks for getting in touch!
It might work! I'd assume that if you roll 7-9 you cannot choose to roll another dice, correct?
What I'd keep in mind is the kind of story I am trying to emulate. What does it represent in the narrative when I roll a Strong Hit and go for the Super Hit? Am I tapping into a source of unstable power that, if I am able to get past its chaotic nature (7-9), I am able to perform incredible feats (10+)? If so, the new tier makes sense, you know?
Mathematically, looks solid!