How are today’s Mormons (LDS), Muslims (Islamists) and non-Catholic Protestant Christians (all 36,000 different non-Christian denominations)
You meant non-Catholic, right? You aren’t actually saying that Trinitarian Protestants, whom your Church admits to be validly baptized, are not Christians, are you?
really that different? After all, they all reject various aspects of Catholicism.
The KJV isn’t a “new” Bible. It’s a pretty conservative translation of the Bible, and in fact it originally included the Deuterocanonical books, though from the early 19th century on most English-speaking Protestants stopped including these books.
The Book of Mormon is new Scripture, but it supplements rather than replacing the Bible.
The Qur’an, on the other hand, is supposedly a more correct and perfect revelation, making the Bible as we have it practically useless in the view of most Muslims (since they believe it was corrupted).
So Protestants reject some fairly marginal books of the OT canon (books whose precise status was disputed by some scholars right up to the Reformation); Mormons add to the canon; Muslims replace it. Three quite different things, though again, all break with traditional/orthodox/Catholic Christianity to some extent!
Edwin