I agree with everything except nr 2 and 3 in the balance section, yes everything, fantastic post.
Trained Units are ridiculously powerful when they level up; 3 units of 5 men in light plate with maces should not be capable of single handedly destroying an entire faction. Played carefully right now, they are. A unit's accuracy and health go up every level. Their damage does not. What that means is that a level 10 unit of 5 will have many many times more hps than a freshly trained unit, identically equipped. Essentially, if you can get a unit 5 levels, they will be very difficult to stop at all simply due to their ability to outlast opponents. They outclass monsters and champions in almost every case once they hit about level 10. I would seriously consider capping their health growth around level 5 so that trained units aren't nigh-invulnerable after they survive three or four fights. This would also make it easier to gauge an army's strength.
Guilden has an amazing array of tools for getting established and consolidating a kingdom. Don't take this to mean that I would like to see them weakened, as I would prefer all the other factions be as solid as Guilden is all the way up from early to late game. So far, all the other Kingdom empires falter in the midgame by comparison, and really only Magnar seems to hold their own all the way up on the Empire side.
Trained units gain way too much from levelling up, we agree on that much, my biggest peeve is the amount of HP gained from levelling though, its massive, and I would not cap it, instead I would lower the amount of HP gained to 2 HP or so, its still huge, but will require double the amount of levels to get to the same craziness as in the current build.
Of course you would have to rebalance HP per level benefits and penalties from blood abilities.
Gilden... What is the amazing array of tools, I don't understand the issue at hand here, I don't feel Gilden does any better than Tarth, and usually Magnar and Karavoxx is the only real enemy AI's. (Magnar because he is powerful, Karavoxx because he have nice start-up powers and robs YOU of your champions, bloody annoying enemy -.-).
AI strength usually depends on where the AI's start, and who is surrounding them.
That said, everything else in your post is fantastic,