@AngryFerret
Yeah, and the existence of mages, even in a very early and unrefined form, also would influence technological development and application on the battlefield in both obvious and more emergent ways. It'd encourage way more thinking about air power of course, "how can we counter/replicate mage effects on a mass scale, or for that matter deploy our limited numbers more rapidly and in top form", pushing fighters/bombers to be much faster and fly much higher. But it'd also have an effect on things like the effectiveness of artillery. Having high quality spotting available in all terrain constantly, 80+ years before the development of drones, would massively change the effectiveness of indirect fire. And that in turn would mess with all sorts of other tactics, and further push "how to do we take out their scouts", so both their own mage forces but also fighters, improved AA, etc.
In a peaceful environment it might not actually change things that fast, historically most militaries were quite conservative and big on tradition by default. But in a great war with ultra rapid back and forth the butterfly effect would propagate pretty quick.