Do you have any references that uav can move a mass with less energy use or pollution? As far as I know they would use more. flight can be more efficient but usually only if its a long distance because take off and landing is energy intensive. Drones fly somewhat like helicopters though which I was under the impression was one of the most energy intensive travel means. as far as I know, good to bad wise, its like walk - bike - train - bus - long flight - car - short flight - ships (mainly I think do to how they are powered. sailing or electrified may be way better) - and helicopter would be at the worst level of pollution.

I don’t think so. While the 3rd dimension seems to grant more freedom and space to move, each vehicle uses more energy/payload, so you will need more vehicles, which in turn fill up the newly won space. Also, in unclear/dangerous situations a vehicle in the 2D-plane can safely stop. In the air, they can’t. This solutions will be restricted to special circumstances and us cases, not for day to day business in my opinion.