I’m not sure where the idea came from of “kinder and gentler” Vikings. The sacking of monasteries and churches and coastal towns is well known. I’m not at all surprised they were brutal to slaves.
Don't you know that our ancestors had nothing better to do with their time then make parchment, ink and pens and spend their time writing down horror fiction about people who did them no harm?
I can see reading some historical accounts with a certain amount of skepticism but the "modern" way is to regard all written accounts as outright lies unless there are major archaeological finds that firmly support them.
Wasn’t there a standard prayer that ended: and God save us from the wrath of the Northman. Does anyone know the original.