Its not true, escape velocity from the surface is theoretical.
Case 1: no atmosphere, v = a * t, peak efficiency is when v is at the surface, rotation velocity at surface is pretty much trivial. since a is not inifinite you have gravity loses while accelerating. If it takes 5 minutes to raech MECO, then you are fighting and loosing energy due to 'hovering' over the lauchpad while trying to reach a velocity at that sltitude that allows escape.
Case 2. Atmosphere, same acceleration constraints, but you ha a maximum dynamic pessure and at that you are losing x amount of energy to drag.
So lets say Vescape is 11500 to escape the total energy you have is 1/2 11500^2. You can add to that energy loses due tongravity which is going to be something like gh for the period of time under acceleration, then the energy loses due to drag. You add that up multiply by two and take the square root and you get a delta v.
If you are in orbit escape energy is the circukar orbital energy times two. So that if you are in a circular orbit, a single ideal burn represents a dV 0.414 x stable orbital velocity. So lets say you are orbiting the mun at 550 m/s and you want to leave the mun you need about 230 dV to leave muns orbit. Now lets say you want a deep orbit, you don't burn all of that and you burn a few dV to circularize to remain. Of course this is fantasy because you have la grange points and other troughs in the gravity wells you can slide through. So the n-body problem shifts this. The game it a bunch of serialized 2 body problems.