The laws of physics describe outcomes as a consequence of the properties of the masses and energies involved. I don't see how you can "set relativity aside", and submit that his theories were only about effect, and provide no insight into cause.
Just going off of Einstein's own words. Einstein very much knew that there had to be something important missing in his theories. He felt that he could predict outcomes, but he could not rectify his predictions with other outcomes. Much like saying, "If you pat your head first, the ball will land on black." If the ball does in fact land on black when you pat your head, that is useful information. But it would be even more useful to know why it will land on black.