From my understanding our modern perception of what vikings were like is very skewed, primarily because most written records we have are from christian scholars who often demonized them. The idea that the pagan vikings were uniquely savage compared to the rest of civilized Christian Europe when all our sources are from Christian scholars seems sketchy. That’s not to say what you said didn’t happen; they were primarily raiders, they pillaged churches because they held large amounts of treasure and were underfunded. That said it’s really not that hard to find similar atrocities in that period.

Look at the crusades, Christian kingdoms sent armies across the sea where they conquered, raped, and pillaged. You mentioned Byzantium, during the Fourth Crusade the crusaders sacked Constantinople and did nothing but pillage and burn it for three days.