I'm not sure that the use of magic significantly changes how things play out since most don't have magic and technology is still a large part of how things are done. Medics can't do their work without medical supplies for instance. Guns, bullets, grenades, food, etc. still need to be manufactured and transported to the front lines. Magic bombardment squads can be killed or run out of food so they're not inexhaustible. Even if someone has talent for magic, it takes time to train for it (for instance, Touri may be able to use healing magic, but she has started out with a small mana pool and not knowing how to do it or create shields with magic). Mana pool also limits the scale of magic destruction; once you develop rockets or nuclear bombs, does a magic bombardment squad even serve a purpose?
So yeah, the magic is just another tool in the war but its effect is not exactly unique and can be replaced by other tools to wage war. The scale of the conflict, and the number of casualties, actually depends on the size of the economies in conflicts.