Protestants and Catholics didn't disagree as to the number of gods; Christians and Mormons do. (Sorry, but polytheism doesn't qualify as "Christianity" any more than it'd qualify as Judaism)
Protestants and Catholics didn't disagree on the Scripture laying out Jesus' basic role in relation to salvation; Christians and Mormons do (Sorry, but the Mormon redefinition of Jesus as a "saved being" and Mormons in general as fellow saviors alongside Jesus doesn't qualify as Christianity)
Protestants and Catholics didn't disagree on the Scripture laying out mankind's role as adopted children of God through Jesus Christ; Christians and Mormons do (not only do Mormons say we've been children all along due to a made-up "pre-existence," but Mormonism = adopted "gods" who will know all things and have all things subjected to them. (Sorry, that's not Christianity)
Protestants and Catholics have always agreed that the end game was living eternally with Heavenly Father and Jesus Christ; Mormons somehow think people can be "saved" in a lesser degree of heaven and never be reconciled with the Father. What? That is "salvation?"
Maybe you missed the point. Protestants & Catholics disagreed on who was Christian for centuries. You’ve named many differences between LDS & “Christians”. There many differences between Catholics & Protestants as well such as authority, baptism, faith vs. works, etc.
I guess the point is, what makes you more authoritative on who’s Christian, than the Catholics who claimed likewise for centuries? Because LDS differ on Christian dogma?
If a Catholic confronted you & claimed you weren’t Christian because you don’t accept the Pontiff & the line of Authority, or because you don’t believe that works are part of the saving process, as they did for centuries, would he be correct?
Christians have killed each other for centuries over these very points. Seems like kind of a ridiculous argument to me.