I got this game pretty recently. And to be honest, it's quite awesome! But it can always improve.
To add something new, we'd go on something like this:
Eagger defense quests: Brigand patrolls of some kind, weak, small orc raids. Maybe 10-12 batallions?
"Medium" defense quests: You get as a viable target for the local lords, so they try to raid you with bigger armies. Maybe 30-35 batallions?
"Advanced" defense quests: At this point in the storyline you've slaughered cities and half of a race, so you're attacked by large armies. Full sized armies?