Saturn V had to climb out of a MUCH deeper gravity well than just to the ISS LEO.
Still, a magnificent accomplishment, especially since it was 45 years ago!
When we did a tour of the Cape years ago, the guide showed us where the one of the control computers was mounted on an intermediate ring between stages. I asked what the equivalent computing power was.
"Oh, about that of the original IBM PC."
These rockets are for the little module that gets into orbit, not the heavy first and second stages. All this needs to do is take the small capsule out of orbit, and slow down from terminal velocity to zero.
The ultra-heavy lift vehicle that will send SpaceX’s Mars Colonial Transporter to Mars will have 27 million lbs. of thrust at liftoff (maybe a little less).