Let's break this down...one word and one phrase at a time.
First of all, you are sadly mistaken if you think Mormonism teaches that Jesus is THE Son of God -- as if Mormons don't also think you're a son of god, I'm a son of god, Satan's a son of god.
Because of the Mormon teaching of the so-called "pre-existence," they believe ALL men were spirit-babies -- "sons of god" -- near Kolob.
So -- what then makes Jesus unique among BILLIONS AND BILLIONS AND BILLIONS of sons of god per Mormonism? The phrase "the only begotten"; but even then you need to understand that doesn't have anything do do with Jesus being THE Son of God from eternity past!
When Mormons use the term "the only begotten," they mean that in connection with Mary only. The Mormon Jesus only became God's "only begotten Son" upon conception within Mary. That stands in contrast to THE Jesus of the Bible as THE Son of God from eternity (John 17:5) -- having shared God's glory before the world was -- is God's one and only Son (John 3:18)...the rest of us are mere "adopted" sons -- if we are indeed His.
Finding perceived doctrinal differences in the minutiae doesn’t change the fact that Mormons have a fundamental belief that Jesus is the Christ. And because Mormons hold that belief they easily qualify as Christians. I will agree that Mormons belong to the restorationist branch of Christianity which is different from reformationists, but they are both Christ centered faith systems.