Apart from their different 19th and 20th century foundings, Mormons and Moonies do have striking similarities. Both religions' founders, Joseph Smith and Sun Myung-Moon, claimed special revelations which called them to complete Christ's derailed/unfinished work by (re-)founding the Church, both penned a post-Biblical scriptural corpus (Smith's Book of Mormon, Doctrines and Covenants, Pearl of Great Price and Moon's Divine Principle), and both center their morphings of Christianity around marriage as the condition for salvation*. Both reject the Trinity: Smith's physical Heavenly Father, who was once just a man himself and grew into Godhood, joins an (unnamed) Heavenly Mother to produce the spirit children who eventually become incarnate in human bodies, while Moon asserts that the incorporeal Father joins with the female Holy Spirit to jointly parent the souls of the redeemed human race. Both groups avoid using the Cross in their religious imagery.
Even the ultraliberal National Council of Churches declared the Moonies non-Christians.
If by both historical standards and by contemporary count, 95% of Christian churches have taken the Incarnation of Christ as Divine/Human Son of God, plus the recognition of the sole Deity as a communion of Three --Father, Son, Spirit--- as fundamentals, once you break those central and linked beliefs, how do you maintain that your religion is still Christian rather than post-Christian?
*Another somewhat similar post-Christian church is the New Church of Emmanuel Swedenborg, who influenced William Blake and Carl Jung. Once again, a seer of special revelations far outside the historic Church, a large quasi-scriptural corpus and a special interest in marriage as the vehicle of salvation.
Swedenborgian sanctury in Pennsylvania
For Christology, the NC holds that the One God Jehovah became Jesus Christ. No Trinity. Mormons hold that the Old Testament God Jehovah is Jesus Christ in the New, with the separate Old Testament God Elohim (which the orthodox take as a synonym) as his Father, but they are separate "personages" with physical bodies.
And then there's the once very visible but now dwindling Christian Science Church. Again, post-Christian. No Trinity, no Incarnation. A post-Biblical text from a New Thought founder(ess) who resurrects the lost doctrine and reality of a spiritual Christ. Here, marriage, while honored, plays no central role in the mythology, which is entirely focused on mind-based healing.