others were directed by Lawerence Kasdan and somebody else
Irvin Kirshner. Actually, I think Lawrence Kasdan wrote the screenplay and was a producer, not a director.
Also, Steven Spielberg had quite a bit to do with Return of the Jedi. It was directed by someone whose name I cannot pronounce, nor recollect (and at this sad point in my life, I do not own the original trilogy
, so I can't look it up.)
But, in any case, the point is well taken, and spot on. George Lucas is not a very accomplished director, to the detriment of the new trilogy.