And it's not like the quality suffered for it once Episode V was released. You can make the argument that the quality suffered once he got to Episode VI but that's subjective. It was the end of the trilogy anyway. Alot of that film was dictated by the previous film and the lack of technology to accomplish things he wanted to accomplish in Episode VI.
If he really wanted to make sure Episode V made more than the previous film, he would've made the exact same film over again. Clearly, he did not. He wanted to take the world he created in a new direction on all fronts. Sure, he was worried about the financial aspect of the project and how it relates to his grand plans of having his own filmmaking studio up in San Fran., but he clearly wanted to take the storyline and the quality of film to new heights.
That's part Kershner. No doubt about it. But, Kershner's film doesn't work without Lucas' draft of the script before Kasdan got there. That's where the foundation started for Episode V. You take Lucas' contribution to that film on all fronts, and you don't get the Episode V. That's just fact.