A Jedi uses the Force for knowledge and defense. Never for attack.
Luke did exactly what Yoda taught him. He told him to confront his father, he never told him to outright kill him. Ben told him the Emperor would win if he didnt, but Luke was the one who proved Ben was wrong. They wanted him to destroy Darth Vader - and he did, by using the Force to find the good in him. When he went on the attack in ROTJ, he stopped when he realized what he was doing, stopped, and threw away his lightsaber.
He did exactly what he was taught. In ROTJ and in TLJ. There was no asterisk. And even if Luke could find a solution that even Ben and Yoda couldnt see, it proves Yodas point in TLJ, They are what we grow beyond.
TLJ was Lukes time to see that.