We did both cruises in the past (when the BI cruise was still 12-nights). They are very different cruises. The Fjords cruise is similar to Alaska. The highlights are the views you’ll get from the ship and while you are in port, but the shore activities, while fun and interesting, are not memorable unless you are into very active adventures. They added Amsterdam this time, which changes somewhat that conclusion. That port is similar to those on the BI cruise.
I agree that a BI cruise is a convenience cruise. The sights from the ship and navigation are nothing to write home about, but you get to do significant cultural visits every day while not having to drive or pack your bags.
Our BI cruise is certainly our best cruise ever, but the itinerary and duration made it a very different cruise to what will be offered in 2023. We got to see the Orkney islands, the Salisbury cathedral, the book of Kells, Penny Lane and Stawberry Fields, etc. Based on the 2023 routings, we would probably pick the Norway cruise.