There’s no evidence Oswald was a fall guy. Wondering why things were one way or another is not evidence.
As for evidence, due to the lack of a trial for Oswald, the only evidence that can be offered that of an incomplete historical record. That includes the views of those in a position to know.
As I pointed out, most of the Warren Commission members and numerous credible political figures believed that Kennedy was killed by a conspiracy. Indeed, LBJ browbeat Earl Warren into chairing the commission by telling him that there would be a nuclear war unless the public and the world at large were assured that Oswald was the assassin and acted alone.
As LBJ explained it to Warren, Oswald's trip to Mexico City indicated that he acted at the instigation of Cuba and possibly the Soviet Union. On other occasions, LBJ confided that "Kennedy tried to get Castro, but Castro got him first."
Yet others with knowledge of the facts have placed the CIA, the Mafia, Texas oil interests, or LBJ himself at the center of the conspiracy. Plausibly, these disparate elements might even have been knit together into a conspiracy based on shared hatred of Kennedy. Eventually we will know, perhaps by the release of official documents or by revelations and proof from an unlikely source. Time will tell.