The twin story arcs of the Three Nephites and the Apostle John never tasting death create a massive continuity problem for the restoration narrative.
If immortal, doctrine and priesthood-carrying sentinels have been wandering the earth for over 2,000 years, then there was never a full apostasy. And if there was no apostasy, there was no loss of priesthood authority. Which means there was no need for Joseph Smith to restore much of anything.
No need for the Book of Mormon. No need for the "restoration" of sealing keys. No need for most of what Joseph Smith served up—especially the illegal unions with teenage concubines or conjugal relationships with other LIVING men's wives.
It's almost like the whole thing was made up and well-meaning but gullible people susceptible to the next shiny object bought it.