MTW preferred unit size?

[Ludens]

in reality you could do that so why not in game?

In reality, medieval kings called on their vassels to provide them with pre-trained armies. They did not train them one by one. None of the TW games comes close to simulating how troops were levied. I agree that upkeep is a problem for the A.I., but I play MedMod where it is less of an issue. I did not notice any serious problems with A.I. army size and quality, or at least less so than in vanilla. Still, it is quite long ago since I played with normal unit, so I cannot really make an comparision.