I had that issue too! I solved being stuck on the guy by taking 4 of my orcs and sending them to kill him for me. Having them gank him really helped. I think two of my orcs died in the battle but they weren't chosen to survive haha.
I also similarly got stuck on a particularly nasty Warlord, so what I ended up doing was getting 3 of my Epic orcs assigned to 'bodyguard' the warlord, by sending them to infiltrate on him... so when I got into the throne-room to fight him, my 3 dudes turned on him and helped me wreck his face!
Sometimes ya just have to change the conditions of the battle to be in your favor!
OH wow, I can't remember that being a thing. It's been a couple of years though. This made me want to go back and play it again. I might just have to pick them up the next time they're on sale.
It's WELL worth dropping some time into for a bit of fun casual gaming!