Describing that story as a “relationship” developed over three movies is mostly untrue.
I see it this way:
ANH: Vader (together with Tarkin) is the villain who killed Luke’s father and his mentor.
TESB: Vader captures and tortures Luke’s friends to get him and later reveals to be his own father.
ROTJ: Luke is said to defeat Vader, yet their conflict relationship brings them together and overthrow his master.
To me, it’s all about their relationship, one way or another.