So airstrikes aren't an unfair advantage?
Fine if no stips can be changed that means wizards all have imperio amps. Every wizard is thus at peak proficiency (at least Vold level), which means all can teleport with a thought and cast fiendfyre with a gesture
Wherever the military's base is, the wizards can teleport in, cast 5 fiendfyres, and then it's a wrap for the military command. They could teleport into the airplanes, AK the pilot, and teleport out. they have Vold-powers so they can fly. They have shield charms, telekinesis, can mind control, transmutation of enemies into mices, etc.
ANY military deployment will get eviscerate by fiendfyres, and since there are no stips, and everyone has Vold-level power, they can spam the military with hundreds of fiendfyres and the military will be obliterated.
Normally, they would be limited due to their skill level, but since there are no stips, every character is imperio'd, which means that they can do anything Vold wills them to, even that not physically possible normally.
Vold and his army win. If you claim the military win via air strike, that only proves that the wizards are so powerful that the only way to defeat them is to destroy the entire city they are invading. Either way, wizards come out looking badass here