And frankly, I wouldn't be half shocked if Yoda told Luke that to give him extra incentive. It may have had nothing to do with really becoming a Jedi.

What did Luke accomplish? Resisting the dark side? He already did that in ESB when he faced death instead of giving in. Sure, he was pivotal in redeeming his father, but so? Does every apprentice have an evil father he has to redeem before earning the official Jedi merit badge?

YODA: "You must confront Vader. Then a Jedi will you be. Because. . . uhm. . . reasons."

A few extra lines of dialogue or exposition on the Jedi training traditions could have fixed this.

This aspect of ROTJ isn't necessarily what I would call poor writing, but it is lazy. Like most of the film. Aside from the special effects.

Does that remind you of a certain other trilogy?