Right now no other ship does the 11 day itinerary that includes Fanning Island. Norwegian has a brand new ship running seven day cruises that include Fanning Island but otherwise very few and very short stops in Hawaii. Soon Norwegian will have several new ships sailing in Hawaii but as they will be American Flagged they will not have to do the Fanning Island thing.
You are right, Fanning Island is a fantastic , much different place, but only the Wind does the itinerary that gives you Fanning Island and a full Hawaiin cruise as well.
I have done the cruise on the Wind, and although it is not my favorarte ship, I found the whole cruise to be a great experience.
Actually having cruised and recently done an extended land vacation in Hawaii, I prefer the latter.