I'm surprised at the Norse (or Norway) being in the base game although a lot of Civ choices have been surprising this time 'round.
While the Norse are fascinating it seems their modern legacy in the Anglosphere is one of romanticism. I wonder how they'll be interpreted.
If I understand correctly, the Iroquois Laws were the basis or inspiration for framing US Federal Law, and provided some framework for the US constitution. Considering that the US Constitution is often seen as one of the Wests greatest political achievements, at least one of their achievements had a big influence.
Iroquois symbolism (bald eagle) also became one of the US's most famous and Thanksgiving may have been an Iroquois Tradition long before any pilgrims arrived.
Lastly, when playing world/Terra maps, some historical accuracy can add to the immersion. An empty new world can break it. I don't think adding in a Native American Civ is any different than a Celtic Civ (also famous for being defeated!). Both are romanticised in modern popculture and more embarrassingly neo-paganism.