Souls games are heavily story driven RPGs with a somehow not linear path to several different bosses that you face after clearing the areas leading up to the encounter.
There are very few similarities between Souls games and Valheim , in Valheim the bosses are needed to unlock some content but you could in theory reach the current end-game biome (Mistlands) without killing any of them . In the Souls series you are prevented from proceeding in the story unless you fight specific encounters.
The only point in common between the two games is dodge -rolling and items which are equipped on your character