All that lends itself to proving that: 1) LBJ was not involved in any conspiracy; and 2) Oswald's Mexico City trip was not faked as a pretext for war with Cuba or Russia. The conspirators would not have gone to the enormous risk of assassinating the president without some assurance that the person who would replace him would be onboard with their objective.
1 - LBJ was deeply involved with the intelligence and political coverups after the Kennedy assassination. RFK Sr too. But it doesn't prove that he was involved in the conspiracy to kill JFK. And of course, I don't believe RFK was in on a conspiracy to kill his brother. The conspiracy and coverups that followed the assassination should be viewed as two distinct things. The motives for the coverups might've been related to avoiding a war or covering up illegal acts abroad (ie assassination attempts in Cuba) moreso than protecting potential conspirators.
2 - The Mexico City trip makes no sense outside of the context of it being some sort of intelligence operation. Oswald, having visited the USSR previously, knew of better ways to be able to travel to the Soviet Union or Cuba. Maybe the point was just to make a scene so it could be documented that he (or someone pretending to be him) visited those embassies weeks before the assassination? Or maybe it was as John Newman and others theorized, an attempt to create bad PR for the Fair Play for Cuba Committee?
We simply don't know enough to conclusively say what happened in Mexico City...