I'd disagree. ROTJ makes a great point in stressing how potentially close Luke is to the Dark Side. Not in oblique ways but in ways that are notable enough. His actions during the duel with Vader become his final test. And he falters but then recovers.
Without a moment like this, the moment when he tosses down his lightsaber loses all narrative power. As it stands, that moment is the defining moment of his character and of the entire IPs philosophy and morality.
No I agree on that, but what irks me is that Luke said if Vader went all out he would have been flattened. Rest of its fine.