I read once where the key to advanced flight propulsion is to eliminate gravity around the vehicle, via on board electromagnetic generators. Then propulsion requires only a small force.
I read something similar. Back in the late 1980s. I think a couple Canadian scientists were working on electromagnetics on metal spheres, having them spin rapidly. The enclosure including the metal spheres appeared to become buoyant and rise by lessened effects of gravity. They claimed they were defeating gravity and would soon have working anti-grav engines. I didn't hear anything later on about them, in the 1990s or since the original articles. Filed it in the back of my mind along with fusion energy and traveling to Mars soon.
I think that is mostly true just for takeoff situations. Think about a glider, they have zero thrust, yet they can stay aloft for a long time, just through aerodynamics of their design. They just cannot get up in the air without external power.
So, if you could eliminate gravity, you could takeoff with very little power, but you would still probably need about the same amount to generate the same speeds through the atmosphere. Your main enemy is going to be air resistance at that point, not gravity.