Taking a metered taxi and getting charged the flat rate beats the purpose of queuing up for it.

FWIW, I usually take the zone based flat rate taxis (I just learned they are called coupon taxis) when I have a lot of luggage and don't want to carry them all the way to the taxi line. It's fixed rate per destination/area, there's usually no line and they tend to have nicer cars. It's roughly 1.5-2x more expensive than regular metered. There's also no incentive for the driver to take the scenic route as they get paid per trip and they want to get back to the airport to get their next pickup.