My point is simply that you can't subtract the velocities of the two planets and call that your delta V. Delta V is the amount of actual powered acceleration yo

My point is simply that you can't subtract the velocities of the two planets and call that your delta V. Delta V is the amount of actual powered acceleration your rocket does, which is only very indirectly related to the differences in velocities between the origin and destination planets. For example, to get from an Earth-like solar orbit to an asteroid orbiting the sun very far away, at nearly 0 velocity, you'd need nearly solar escape velocity at 1 AU, or about 42 km/sec, minus the Earth's 30 km/sec. Even without taking advantage of gravitational slingshots or the Oberth effect, the delta V requirement is 12 km/sec, not 30 km/sec. So subtracting velocities has nothing to do with delta V.