[magnate]

For my twopenn'orth I don't think your problem is with mages (though you may not be using them optimally). If you are still getting stomped by the AI's massive armies of chaff in the late game then you need to build more SCs. A single SC pretender can only take (or hold) one province per turn - by the late game you need a few more. If you equip them with flying boots they can zip around plugging holes your armies cannot reach, or zooming in to attack behind enemy lines.

So what is an SC? Well there are people far better qualified to answer that than I, but the easiest to acquire seem to be the six Ice Devils (Blood 5, 55 blood slaves each). If you don't like mucking about with blood hunting then there are ten elemental monarchs (3 Air, 3 Water, 2 Fire, 2 Earth - all Conj 7). The AI rarely summons any of them. Equip any of these with good weapon(s), armour, hat & misc items and they can take out whole armies on their own. There are tons of threads discussing the best equipment for the different SCs. Even a Bane Lord (Conj 5, very cheap) can take out small armies if it is properly equipped.

Of course, SCs require a whole boatload of mages to research construction and then actually to make the items, so they're not trivial. Despite this, many players frown upon the use of SCs against the AI, because (like undead hordes) it does not defend against them at all well. There are "anti-SC" strategies which human opponents will use but the AI will not.

Finally, don't forget that the AI does not build castles (though it occasionally obtains extra castles from random events). When waging war on an AI nation, take its capital (and other castles) as quickly as possible, because it will then be unable to recruit its best units. The rest of its provinces will then fall easily.

Good luck,

CC