All religions defend their peculiarity and uniqueness, but in reality all of them feed on the beliefs, myths and rituals existing in their environment.
There is a theory held by many authors, certainly simplistic, that helps us to understand some of the complexity of the Greek religion and, by extension, of the Roman one. It is the theory of the two sources. During the second millennium BC waves of northern Indo-European peoples, with a pastoral and patriarchal culture, entered the southern Mediterranean peninsulas with agricultural and matriarchal culture. This mainly explains the creation and evolution of Greco-Roman religion.
But, along with the theory of the two sources, we should certainly join the many influences of the East, of Mesopotamia, Egypt, Asia Minor, Middle East, etc.. of an area with agricultural myths from four or five thousand years ago.
Actually all religion is a syncretism of beliefs, rituals and myths as precisely reveals the history of religions and mythologies of the Mediterranean countries and the Middle East. So for example, the marriage of Zeus and Hera would mean the forced coexistence of an European male god with a Mediterranean mother goddess.
In any case, compared to some unscientific ideologies that attempt to justify the Greek culture as the exclusive product of an Indo-European component as opposed to the Oriental (which is often identified with the Semitic), we have to maintain an open stance to all kinds of information, and to be critical with any present or ancient source which reproduce the topic of an exclusive Greek rationality versus the surrounding mythical thinking.