Boarding in Istanbul was a circus a couple weeks ago. They really haven't figured out how to make the new terminal work very well. You would assume that if a ship was disembarking that there would be plenty of cabs, but that may not be the case. As you have read the taxis can be a bit of a pain, unless you are getting in one at a hotel. The good thing is with the currency issues even the inflated price is really not that much, just make sure you have a price set before getting in the cab. If you are spending a few days in Istanbul look at the Istanbul e-pass. Not only does it get you guided tours to most of the sites, but if you have whats app you can text them and they will respond quickly with all kinds of local advice. We stayed at the Park Hyatt in a wonderful area that is close to the port.