Yes, that holy strike of yours and the stupid ballista (I should have spent two turns on it) were the biggest obstacles, and of course, the speed... I also had artifacts to reduce enemy defense and luck, but I decided to keep them for myself. It's a pity that the defense and luck were reduced (only 2 luck remained, and the defense was at zero), meaning all the leveling was for nothing, and you can't run away with just one attack and defense, even though I had a decent army. Maybe I was doing something wrong because of my noob status in Heroes 5 (not in terms of leveling, I don't know anything about that... but in terms of combat, because I mostly played duels, and they've simplified these battles, which doesn't give you enough experience).
P.S. I still think runes are cheating because they provide extra magic for EVERY unit and on EVERY turn.