> to me seems like people witnessing the airplane and complaining that it isn't "real flying" because it isn't a bird flapping its wings

To me it is more like there is someone jumping on a pogo ball while flapping their arms and saying that they are flying whenever they hop off the ground.

Skeptics say that they are not really flying, while adherents say that "with current pogo ball advancements, they will be flying any day now"