I agree to your Thesis that Jesus was send as a last Prophet in chain of prophet send to Jewish community. Christianity would not spread if not for Paul ( who glorifies Citification and changed the original message) and later conversion of Constantine to Christianity ( to utilize the power that religion brings) , recently wrote some thing around it

On the flip side Torah followers also did not kept the original text intact and when Jesus arrived they never accepted him as Prophet instead they were looking for a Messaiah who will establish them a rule like David so they conspired to kill him ( hence we see all the Jews persecution starting with Romans toward Jewish community)

In my understanding every religion started as monotheism before their followers turned into some thing else and is of the reason we are all divided and eventually gave a bad name to religion