I challenge that assertion and here's why.
I had a couple of young men from one of the larger Baptist congregations in the area stop by one morning. We had a pleasant chat about their message and invitation to come to services.
Not once, did they mention anything that would indicate to me that my beliefs/church were "apostate", that there had been "a great falling away", if you will.
We were brothers in Christ who held the same views of God and Jesus. How do I know that for certain? Well, I listen to their Pastor's messages on one of the local Christian radio station. It's as if I'm attending services there, yet I attend a Grace Chapel.
Yes, there is "but one narrow path to salvation". Unfortunately, the mormons are engaged in a road widening project with all of the extra "ordinances" they require for "exaltation".
The Mormon road isn’t leading to the same destination as the Christians.
30 years ago Christians used the same message, accept Christ or die and spend eternity burning in hell. Thankfully, Christians have learned to better communicate and are saving more people.
The Bible warns us of false teachers and churches which lead believers astray. The Bible indicates we are each to be wary lest we follow one of them.