You can still have a rocket on your vehicle to accelerate further after take-off, but you certainly need to accelerate less if you already at a certain velocity

You can still have a rocket on your vehicle to accelerate further after take-off, but you certainly need to accelerate less if you already at a certain velocity than if you are stationary. Since the “certain velocity” is free by assumption (i.e. supplied by ground-based electricty generators or something similar), I don’t see how you could be off worse. But I still didn’t do the maths fully.