Yes, one of the conditions presupposed was air superiority, or enough surprise as to realize that effect locally, but an over-riding consideration was the speed with which such heavy war machines could be delivered. The costs of the equipment - in this case the gliders - would be considered very secondary to winning the battle they are committed to. Crossing any bodies of water wider than a decent river posed large problems. The issue of surface transport loomed large in any battle plan. To get an idea of this - but going the other direction, look at the Allied D-Day efforts. The Allies just gave up on air transport of objects over a certain weight and/or size, because it just was not practical, given the parameters of technology available, development time required, and sheer logistical practicality. The German High Command desired the delivery of medium tanks by air, in furthering the overall concept of the overwhelming surprise attack. Shows how steep the learning curve can be, in unknown realms of design!