Ambrosius?

[Metathron]

What good would waiting do?

Since you say he is tremendously stronger, have you cleared out all the previous areas, i.e. all of Kordar and Ellinia? If not, you could probably gain another level or two there.

Also, which class are you playing as? If as mage, then your leadership will be naturally lower, and the game measures that when evaluating the strength of an enemy army, which means it doesn't take spells or stats into account, and these things may easily turn the tide of battle.