I think it’s a misreading of DE that Luke embraces the dark side in the story. Luke is attempting to understand the secrets of the dark side, both to understand why his father turned and as a means of conquering the dark side from within, but he underestimates the sheer oppressive nature of the dark side and comes dangerously close to succumbing to it, but Leia comes in at just the right moment to pull him back from falling into that abyss.
The problem is that Dark Empire basically rehashes something that already happened and was resolved at the end of Return of the Jedi. Luke already flirted with the Dark Side. He was right there on the edge, he nearly killed Vader in anger. That was his moment of temptation, and he overcame it. That was the whole point of his character arc in the Original Trilogy: he saw what his father became, he almost followed the same path, and he chose to stop and throw his weapon away. So when Dark Empire comes along and says, “He flirted with the Dark Side again, was almost about to fall, and it took Leia to bring him back,” it just undercuts everything that came before. It feels like going in circles instead of progressing the story. From a narrative standpoint, it is just not satisfying.
Guess I can understand that position from someone who enjoys ROTJ. I don’t enjoy ROTJ. What you see as a rehash, I see as an improvement.