The historical record will always be skewed, but there's no reason to think it's not largely true as it's repeated even in their own (Vikings') re-tellings. But I'm not even saying they're uniquely evil - my whole point is exactly that there's no real "good guys" in these stories unlike what Ubi wants to show. It's just the way that culture was. I've been reading a bit about them in the past year as I never was much interested in Vikings, but this was preparation for this game & some Banner Saga re-plays.
This has a proper overview of all aspects:
https://www.routledgehandbooks.com/doi/10.4324/9780203412770
Well that I will definitely agree with, there are no good guys in history and indeed no bad guys, every nation is a mix of people and all of those people are a mix of good and bad rather than purely good or bad.
Having said that, as I say, if I was reading up for a dissertation about it I would care about getting it right, or it I was enjoying a documentary on tv I would care about the accuracy of it. But in a video game, I dont. It could be smurfs and rainbows, firing marshmallow arrows for all I care, as long as I like the gameworld and the game mechanics
(Except for that speccy smurf, wouldnt want him in it
)