Exactly. As I mentioned in one of my previous posts, there is no outright conclusive evidence of whether or not Luke is stronger than Vader. Heck, section that you're replying to explicitly says "as close as he's ever come" not "definitively states." It's "as close to" Lucas saying who is better as we've ever gotten, but he's never just flat-out said "Luke surpassed Vader" or "Luke was still weaker than Vader." Hence my two massive, multiple paragraph long posts about all the implied evidence, character statements, ect. Since we don't have official answers (unless you accept that the novel is a valid source), then all we are left with is to analyze everything we see and are told in the movies to come up with as close to an answer as we can.