The belief in the divinity of Jesus as the Christ is completely different in trinitarian Christianity than it is in non-trinitarian Christianity, or Islam.Huh?
I mean, Jesus is Jesus in Christianity AND Islam. Historians believed that he existed.
It is believed that he is/was the Jewish Messiah, born of the virgin Mary etc. etc.
Move past the concept of a virgin Mary, and ask whether she was conceived without sin, or whether she is perpetually a virgin. These are NOT universally held beliefs, not even close to it, even amongst monotheists.
Ultimately, saying that the people of the Book all have some common elements to their beliefs borders on being a truism. Indeed, all monotheists do. How could they not?
I'm unsure why you think that means you are all worshipping the same God. I get that you believe there is only one God, and anyone worshipping a single creator being is effectively paying homage to that, whether intentionally or not. But they are certainly not worshipping the same set of ideals, the same history, or the same divine commands.