There is another overwhelming fact that you're missing too. Fuel costs FC points. If there is only a couple of you in the fc you're going to be hardpressed to maintain one airship let alone 4. There's also going to be content that will only be accessible through airships. Special zones with unique hunts and gathering nodes. If I'm right with the impressions SE has given over the past couple years, you will need disciples of war & magic to protect these gatherers. If you can't fill a party for this airships aren't going to be worth your time.