False. the doctrines of trinitarian Christianity were confirmed 300 years after Christ, but they were held from Apostolic times as orthodoxy.
Christians from the beginning held that:
1. Jesus Christ is God
2. Christianity is the fulfilment of Judaism and there is ONE God
Put those two together and you have doctrines that do not hold to Mormonism or Gnostic views
Catholic bishops in the fifth century -- the Nicene Creed dates from the 300s, what are you talking about the 5th century?
Mormon doctrines are:
1. contradictory to the Judaic concept that there is ONE God
2. contradictory to all that Christians or even heretics have believed since Apostolic times
3. Based on a piece of fiction -- that there were Semites in pre-Columbus America
Pardon the possible thread drift, but I see "Native Americans came from Israel about 2500 years ago to what would one day be the United States" as being no more incredible than "Every animal species on Earth is descended from a M/F pair that rode out a flood on a wooden boat 5500 years ago".