While it was possible for a grade-6 grand mage to win against a grade-7 sorcerer in a fight, killing one might still have proven difficult. The flight capabilities of grade-7 sorcerers were, after all, orders of magnitude above grade-6 grand mages.
No mage would have even considered the thought of Saleen attempting to kill a grade-8 sorcerer.
What enabled the possibility for Saleen to do so, was the devil's armor that Joey crafted for him. The armament was affixed with grade-7 magic, with the two grade-12 magic nuclei etched into the mask providing the energy required for holding the grade-7 magic spells within the armor.
The devil's armor required only six hours to enable repeated conjuring of the magic spells. All other grade-7 spells were used up other than Stone Statue Army. What remained other than that, was the three high level magic spells stored within the wooden sword in his hand.