While I agree with much of the above post it is somewhat spoiled by the last paragraph.
The problem with the development is that it is in the passengers faces rather than hidden away but for Luton it can't be any other way due to constants on the land available and ever rising passenger numbers. Also work can only be done in a set order rather than the most urgent issues being tackled first with at least another years worth of work on the terminal before it is finished.
I totally agree that someone has cocked up big time with the drop off zone which just adds to the long list of bad designs. In recent years we have seen arriving cars having to cross the path of cars trying to leave. A set of traffic lights on the CTA roundabout that only lasted a matter of days and pay barriers on the exist lanes to the drop off zone which would bring traffic to a standstill. I think all of the above has happened in the last 5 years and now we have a single lane with 4 planned pedestrian crossings.
If Luton was flattened it would take longer than 6 months to rebuild it, more like 2 or 3 years and what would happen to the existing traffic? I don't see the other London airports absorbing 15 million passengers.
With work starting on the new station and cut and cover tunnel out of the CTA around the end of the year there is a few more years of work until 2021 before it is all finished.