Personally I think that Mark Hamill is superb in all the original films and doesn’t get enough credit for his acting, from naive farm boy in Star Wars, to a Jedi student in Empire finding out Vader is his father on Cloud City, then to mature Jedi Knight in ROTJ. The dual between Vader and Luke on the 2nd Death Star is easily the best light sabre dual in all of the Star Wars movies, not because of the choreography but because of the rage in Luke.
I agree. If anything, ROTJ suffers when he is not on screen. Ford and Fisher were so no wooden in it. Prowse/Jones are also great as Vader in ROTJ.