He just described the energy requirements: each gram of payload needs 15k of energy put in to escape orbit. He didn't think of fuel which exists simply to move

He just described the energy requirements: each gram of payload needs 15k of energy put in to escape orbit. He didn't think of fuel which exists simply to move the rest of the fuel (the rocket equation). Imagine 50 sticks of dynamite separated by metal plates. The bottom stick explodes, lifting the pile a bit (energy split 50 ways). Then the bottommost explodes, lifting more (split 49 ways). This continues until the second stick propels the first into orbit. You can play with the numbers so explosion energy * (1/50 + 1/49 + ...) = escape energy You quickly realize it gets asymptotic, and extra fuel contributes relatively little to the payload.