I think one of the reasons wwx and lwj could work so well together in the end were their differing journeys in their perspective of control - which (to me) is one of the central themes of the story.
Lwj grew up in a very controlled environment, but he was not the one in charge of his life. He is constantly controlled by the Lan clan rules, as well as the expectations placed upon him as the second Jade of Lan.
Overtime he learns to take control of his personality and actions - defying the clan norms and showing up where there is chaos. His regrets are all about how he let himself be controlled into making decisions, eg. letting Wei Ying go to the burial mounds alone, not confessing his feelings.
Meanwhile, Wei Wuxian grew up desperately trying to find some semblance of control/power. Unlike lwj, he grew up in a household where his role and position drastically changed from day to day - sometimes he was treated as a servant and other times a brother. This meant that in his head, the only way for him to gain some semblance of control was to be consistent and powerful (because then he was useful enough to keep).
This is shown in how he is desperately trying to convince everybody that he is in control and that the events that aren’t his fault are still his burden to carry, because he learnt that he is only worth using (only worth controlling) if he can first control himself.
However, as the story progresses, he learns that not everything was his fault and this slow cede of guilt and blame in what allows him to finally be at peace and happy.
Their character journeys are so different, yet the core of most of their drives is about their perspective of control - whether of themselves or the people around them.
This is full of wildly different points but I hope it makes sense lol.
