Iceland is also very sea oriented. It was a hub for cod and whale fishing by both Norwegian and Portuguese sailors throughout the middle ages and into the modern period. The major language changes that today make Norwegian and Icelandic mutually unintelligible were mostly complete by the 16th century, which is before the period of intense economic and social decline that Iceland experienced in the 17th century onward due to a combination of Danish economic colonialism, waves of black death, and famines caused by volcanic eruptions. I think it would be difficult to argue that remote Norwegian fjords were more remote than Iceland during this time period, or at least not by much.

What about Norwegian and Icelandic though? Norway has very isolated, mountainous pockets like Iceland, and yet Norwegian is at a similar level of complexity as the other continental languages while Icelandic remained more conservative in that respect.