I've watched alot of Vince Palamaras videos. He seems to overplay the idea that security in Dallas was particularly lackluster in comparison to other JFK trips. I think this idea is overblown. The below video shows Kennedy standing up in his limo during a motorcade in California in June 1963. There are also no Secret Service agents on the back of the car.
Perhaps one reason why JFK was not standing up in the car in Dallas was because his wife was seated next to him. And it felt more appropriate to stay seated during the Dallas motorcade. Otherwise he might have been standing up while riding through Dealey Plaza.
