Zompist Bboard Again

So coming back to an ancient (in my life anyway) fantasy setting, I started to think about how magic might be used in warfare. Now I surmise that about 5 in 1000 people have some talent for magic in this conworld. Out of a population (in the Kingdom of Melland, one of my main settings) of approx 1m that makes about 5000 people at any one time with some magical talent. The difficulty in Melland at least is that there is no organised school or anything where you can go and learn so most such sorcerers end up doing a little of fortune telling/healing/mischief etc, although once in a while someone teaches themselves enough to be a real nuisance, gather an army, stick themselves on the throne etc. Last time that happened the sorcerer's son had no particular talent for magic and the traditional elite promptly deposed him.

But further south the Xularn Empire has a population of maybe 50m, so about 250,000 possible sorcerers. Assume that only a fifth (say) live close enough to a major city to get to a branch of the Xularn Guild of Magic and we have 50,000 possible members of the Guild. Even if only a tenth of those are skilled enough to produce destructive physical effects - fireballs and so forth - that is 5000 possible sorcerers who could be deployed in battle.

I'm wondering how this might work. I don't want to make a cadre of sorcerers too powerful, or a) potentially any force arrayed against them on the battlefield without equivalent sorcerous back-up just gets slaughtered out of hand and b) if the opponent does have such back-up, the "normal" troops seem a bit redundant as it degenerates into a sorcerous free-for-all.

Would you deploy a single large force of sorcerers with other types of troop in a sort-of combined arms fashion? Given my technology level this would be heavy cavalry, archers, infantry etc, maybe some early cannon - bombards and the like. Or is it more likely that individual units would have 1-2 sorcerers embedded (a healing specialist and a fireball specialist maybe)? I can see advantages and disadvantages either way.

I think this would depend very heavily on the details of how magic works in your world. Could you explain that further?

It all depends on how you make magic work: how powerful it is, how much skill is required, what costs there are, what defenses are available. If your sorcerors dominate battle and you don't want them to, give them some sort of limitation.

I'd also note that if Country A has a major military advantage, Country B will do everything it can, including reorganizing itself completely, to counter that. E.g. if you have horse nomads nearby, you split mountains to have your own cavalry— or buy off the nearer nomads. That's basically why medieval Europe had an aristocracy which acted as a permanent, well-trained cavalry. If the southerners can wield 5000 military sorcerors, the northerners need to create their own.

Magic is often treated (e.g. in video games) as essentially free: you can stand there and cast Fireball all day long. That's a huge military advantage over the bowman or cannoneer who will eventually run out of ammo. So one approach is to add a significant cost.

Another is defense. Can you put up a magical shield? Then the attackers' magic is blunted or eliminated.

A lot of magic systems come up with some systemic flaw— a popular one is that for some reason they can't handle iron. So the sorceror has to run away if someone runs up with a steel dagger. With the right choice of flaw, there is room for a conventional army.

How do the Xularn emperors protect themselves against sorcerous usurpers? Or is that what they are themselves?