What I’m saying is that Christianity came from Judaism ....
Your analogy comparing different brands of GM cars is false. The analogy would be that a group of GM employees left, built their own factory, and began making cars. At the same time, they hired a bunch of ex-Ford and Chrysler employees to learn their way of making cars. The new cars are no long GMs, but something different.
As Jesus said, "You do not put new wine in old wineskins."