Well, if the Mormon church is true, then that would mean Lds Doctrines & Covenants 1:30 is also true (it proclaims that the Lds church is the only true and living church on the face of the earth) Hmm what then does that make the Protestant, Catholic, and Orthodox churches per Mormonism?
If the Mormon church is true, then that would mean what it labels about all Christians that were apostate and corrupt and embrace 100% creeds deemed abominable to the Mormon god that also then becomes the true assessment of Mormonism about worldwide Christianity.
If you accept the foundational premises of the Mormon church, beginning with its opening vision, then you must likewise also accept their evaluations of Christianity, Christians, Christian denominations, etc.