You are assuming that he would have been subdued, but you have no way of knowing that he would have been. Everyone's attention would have been on JFK and Jackie not him. There would have been mass confusion. He could have even claimed that the shot came from somewhere over there.
Planes have hit buildings prior to 9/11. No POTUS was ever shot with a rifle before JFK. End of story.
Because Oswald did not shoot JFK at Love Field there must be a certain amount of "speculation"about what would have happened. The best we can do is look to other similar examples of an assassin firing at someone from a crowd. Sirhan, Squeaky Froamme, John Hinckley, Arthur Bremer, etc. All apprehended at the scene. But you didn't answer my question. If you are claiming that because no one had used a rifle to kill a president before 11.22 that somehow casts doubts on Oswald's guilt, then why doesn't that same logic apply to your fantasy conspirators? No conspirator had ever used a rifle to assassinate a president before 11.22. Right? So does that mean that no one could have thought of it because it had not previously been done? And that JFK was not assassinated? That is the only conclusion that can be derived from this bizarre line of argument.