Also likely that this was needed to construct a back-up story of Soviet involvement in case the LHO as the lone nut assassin story did not work.
Plots of this magnitude have to have back-up plans for the back-up plans.
Quite true. A capable conspiracy would engineer multiple stories to confuse and exhaust investigators and the public. In addition, the Warren Commission was deeply compromised by its reliance on the work of the FBI and a directive from the Department of Justice and LBJ to the effect that Oswald was and was to be proven a lone nut assassin.
Indeed, the lone nut assassin story line is so effective that it worked as the official story as to not just Oswald, but also Jack Ruby in killing Oswald. And it was used again as to the murders of Robert Kennedy and Martin Luther King.