The only weapons worth using in that war would be intensive planning, and fast assault. Your guns can just kill or wound. A wizard could transmute your nice powerful tank into a nice fluffy puppy, or suddenly flood a valley that an important squad is travelling through, all with one compact, lightweight weapon, a wand. Their only disadvantage would be that you can fire a gun just by pulling a trigger, within a split second the bullet reaches it's target. A wizard has to speak an incantation and do some kind of wand movement in order to "fire".
You plan entrance points in raids to take out the maximum amount of enemies in the first wave, while no one knows you're there. Then it's just sweep and clear, as fast as humanely possible. Every second a single wizard is unaccounted for in that building, the likeliness of a massacre due to the attack speed advantage being lost increases.