Evidently, you think it is.
Others don't agree.
I think it is a bit suspect. You are quite correct, of course...Catholics do have their extra books, as well. But they, at least, can point to the ancient manuscripts. No mysterious angel uncovered these ancient scrolls for them, and then quickly whisked them out of sight, lest anyone else should copy them.
Mormons claim that their book was inscribed on plates of gold. You'd think that metal plates would wear very well...but, for some reason, these particular plates cannot be found. The same angel that brought them to Joe's attention seems to have hidden them again. But before he did, he allowed several members of Joe's family to inspect them...and they all signed a document to prove it.
The unfortunate FACT that archeology has yet to find even ONE site named in the BOM sort of clinches it.
The Book of Mormon, it seems, is fraudulent.
But all of that is actually secondary.
To be a Christian, one needs to believe in the divinity of Jesus Christ.
Mormons, it seems, have a problem believing in the Godhood of God. Evidently, they think God is a man who hales from a planet near a star named "Kolob", who became a God by dint of His devotion to the God of that world...and, if we are very, very good, and devote ourselves to Him, why...we might even, one day, get to be "gods" ourselves, and have our own planets to rule!
But only if you make sure to wear the right underwear....