Question on battle turn limit

[Olm]

I had heard of this, but never bothered.
I probably should have.

I had a fully kitted Ettin attack an army of ~200 guys.
As I expected they could barely hurt him and with regeneration 13 he didn't bother the very few hits.

So he was happily chopping away on his enemies, clearing one tile most of the time. Suddenly the message came, that my army was routed. I could not understand how that happened, as the Ettin was my only unit on the field, and he was berserk, so who routed? Since he was berserk, he didn't bother and continued chopping until a message told me my enemies were routed. Soon after the Ettin shared the field with only a few decaying undead, when he finally disappeared and the battle ended with a victory for my enemy.

I guess there is no way to change this unfair result, but at least I want to understand the game mechanics behind it, so I not again loose >70 GEMs worth on such an event.

And does that mean I can not use berserking thugs/SCs, or for example Golems against large armies, if they don't kill fast enough?