Guts is the main character and THE point of the series: He's a human who's so inhumanely seeking to become stronger that he slowly but surely surpasses human limits.
In Vinland Saga, EVERY person who's Important has super-human strength to the point where I had to laugh out loud (Thorkell throwing stoned all the way abive the river onto the enemy camp? Lol).
It's literally polar opposites:
Berserk: grounded world with some fantasy
Vinland Saga: fantasy with the visual coating being our real world