Yoda isn’t interested in Luke confronting Vader as a military target.
He wan’ts Luke to confront his fear and conquer it. His fear is he will become Vader and he almost does by following Ben’s line of thinking. Instead (going by the sequels) he becomes Ben which is a bit of a shame.
Again, what does that mean? If he’s just confronting his fear of becoming Vader then that does not require any actual confrontation with Vader himself.