The real moron of ROTJ is Vader. In ESB, he wants Luke to join him and overthrow the Emperor. He's plotting and subversive. All of a sudden in ROTJ he doesn't want to pursue that any more. He's just going along with the motions and doing what the Emperor asks. To top it off, he knowingly delivers a replacement apprentice to the Emperor. All this because "the power of the Dark Side" compels him to obey. Um, okay.
Hah, true. I guess this is the sorta thing you get when George Lucas writes stuff halfassed, right?