Dual-wielding was indeed popular and useful for duelists, pirates, and skirmishers, vikings included. Vikings in particular used small axes to hook into an opponent’s shield so they could thrust with their sword.
Not to downplay your comment, but I feel it’s worth stating that the vikings mostly used that tactic when doing raids, the big advantage surprise. In the darkness with no warning, you can get close enough that everyone doesn’t have time to form up into a line with archers at the ready. Some people might not think that part through.
Oh yeah I agree. But like I said, vikings mostly WERE raiders. They didn’t go charging into actual ‘battle’ often.