Funny how you mentioned you'd be fine if it was just farming, because that was the original idea Yukimura came up with. The idea of a slave travelling the world to Vinland was his initial pitch, but his editor said to him "Well that's not going to sell! A story that starts from being a slave? I thought this story was about the Vikings and fighting, and you're not going to go into that?"
Yukimura considered the feedback and actually agreed with it, so he added the Viking violence into the story, and subsequently the prologue arc. In the end it's for the better imo, as the current arc wouldn't hit as hard if the prologue hadn't happened.