[CelestialGoblyn]

I'm not very experienced, but in my opinion all those could be done:
-Lower all armour's encumberance. Justify it with Ulmish armour being of higher technology than others.
-Give them some affordable bowman unit. If they're a nation of humans, why would they ignore the obvious advantage of having bowmen support the arbalets? Maybe something similar to LA Ulm's villain?
-Give them a good standart bearer. It will boost morale and be thematic.
-Give their priests a national anti-magic spell that would stack with 'tempering the will'.
-Increase the resource bonus in castles
-National Construction summon - steam golem.

edit: And how about a non-magical commander that can heal troops? A field surgeon perhaps. The same guy could also provide a supply bonus.