Very interesting, thanks for the post.
I think the interview very much reinforces my long-standing views of Lucas & Star Wars. We got lucky in 1977 because Lucas had to defer to other people's thoughts and ideas regarding the final film (Marcia & Kurtz), even though he didn't want to.
As soon as he had the money and the power, he went about ruining the stories the way he originally wanted to ruin Star Wars (and eventually did in the late 90s). His power-unchecked was the downfall of the franchise.
The opposite of that (his being 30% of a franchise) is exactly why the Indiana Jones franchise hasn't suffered. He can't have final say, so his stupid ideas (formations of saucers chasing Indy across the desert, everyone he's ever known at his & Marion's wedding, etc) are squelched. Probably has a lot to do with why the four films haven't been altered every few years.
Omnipotence - bad
30% partner - good
Of course, the downside to the partner deal was that it took 20 years for Lucas to quit stomping his feet and holding his breath. We could have had two more adventures during that time. Bonehead.