I would argue it is a distinct religion as they have a scriptural canon which is entirely unique to their church. Unlike simply the Bible (both Old & New Testaments) which is the sole scripture used by all Christian churches, Mormonism includes the Book of Mormon and other texts by Joseph Smith which are common to their religion but not to any other, while also using the Christian Bible. This is similar to how Christians use both the Jewish Scripture and their own New Testament which is unique to their religion. There are also many distinctive theological beliefs of the Mormons that are at odds with Christian teaching. For what it is worth Mormons do not accept non-Mormon baptism nor do non-Mormons accept Mormon baptism. This puts Mormonism and Christianity farther apart than just Catholic and Protestant churches are.
No denomination accepts other denominational baptisms, including Orthodox to Catholic or Protestant. The entire point of each Christian denomination is that they have the truth, and they alone.
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