Star Wars Purist said:

You are right. The dialogue from Star Wars (and Return of the Jedi) suggests that Luke's father/Anakin and Ben/Obi were equals rather than master-apprentice.

BEN: A young Jedi named Darth Vader, who was a pupil of mine until he turned to evil, helped the Empire hunt down and destroy the Jedi Knights. He betrayed and murdered your father. Now the Jedi are all but extinct. Vader was seduced by the dark side of the Force.

BEN: When I first knew him, your father was already a great pilot. But I was amazed how strongly the Force was with him. I took it upon myself to train him as a Jedi. I thought that I could instruct him just as well as Yoda. I was wrong.