Wow’s business model makes more sense than Norweigan’s. Wow takes advantage of geography to offer relatively short flights between KEF and the U.S., with European connections, which allows for a cost advantage using narrow body planes, without pushing them to their limits (in most cases). Other than an established carrier like Ryanair or JetBlue jumping into some O/D heavy East Cost US to Western Europe (BOS/JFK/PHL/IAD-LON/DUB/CDG/LIS/BCN) routes, which they have not shown much inclination to do, a stop in Iceland is probably the only reasonable way to operate discount flights over the Atlantic.
Norwegian just seems to throw darts at the Trans-Atlantic dart board. Without a centralized hub, Norwegian is completely dependent on O/D traffic. Wow’s hub at KEF allows them to penetrate secondary cities like CVG, CLE, PIT, IND, etc, and also offer low cost competition in fortress hubs like DTW, because they are simply in the business of getting people from the U.S. to Europe and vice/versa. Wow has expended operations at CVG before their maiden flight, I have a hard time seeing Norweigien being able to be competitive in the same market.