It’s never a good idea to use the word “cult” when you’re asking about the theological basis of a religious group. Some people use the term to talk about theology, but as least as often people use the term to describe how the group restricts its members in social ways so as to avoid contact with other groups’ religious beliefs. There’s no simple matching between the theology and the social restrictions. I don’t think that the OP really wants to discuss the social restrictions of the Mormon church though. I think that what the OP is asking about is the theological beliefs of the church.
I consider there to be four significant (present-day American, at least) religious groups which think of themselves as Christian, although most Protestant, Catholic, and Eastern Orthodox churches think of them as not being really Christian - Mormons, Jehovah Witnesses, Christian Scientists, and Unitarians. Each of them is clearly at least an offshoot of Christianity, but each of them has significant differences in theology with other Christian groups, differences which are well beyond the differences between the Protestant, Catholic, and Orthodox churches. I would say, in fact, that Mormon, Jehovah Witness, Christian Scientist, and Unitarian beliefs are sufficiently different from other Christian beliefs that I would classify them as Abrahamic religions but not Christian ones. In other words, I would say that they are no closer to Christianity than Islam or Judaism is, but they are closer to it than Buddhism, Hinduism, Taoism, Shintoism, etc. are.
However, you are never going to get a truly objective answer to the question in the OP. There is simply no way to objectively define what the core beliefs of any religious group is. There is simply no way to objectively define how far apart the beliefs of two groups are. Even if there was some objective way to do either of these things, that’s not what most people think about anyway. When the average Protestant, Catholic, or Orthodox person who attends church but doesn’t have significant training in theology is asked whether the people who attend the Mormon church in his town are Christians, he doesn’t usually try to go through a list of theological beliefs. Rather, he uses more superficial comparisons. He will simply note whether the Mormons seem to talk and act like members of other Christian groups.