@nprofile1q... Yes, this is true.
But we're far enough away from the sun to not have to worry about the influence quite as much.
There's nuance when working within gravity wells.
So this is why they have multiple burns on the way to another orbital body (the 3rd body in that problem). So they compensate for it.
They also compensate for it by simplifying the equations. It's how they got the Voyager Probes to use they planets as a shot.
The moon is our back yard, relatively easy to hit.