No it isn’t because only a very small fraction of the flight (0,00074% for Vallis to MOR right now) are in atmosphere and near a planet. This means way over 99% of the flight are for away from planets where there is no atmosphere and their gravity is negligable compared to the sun.
And because it is in space you don’t have a directional change that costs you energy, you just accelerate, drift and deaccelerate. All in a curve according to the stars gravity.
End of discussion, this thread is about Gateways.