I understand your concern, I want to push back a little.
You're saying it's ok for a faith community to have it's own inside definitions and not applied globally. I actually agree with that. Happens in every religion. Problem is that Mormonism doesn't keep it's "definitions" inside the group.
LDS explicitly believe the gospel is universally binding. That's a foundational belief isn't it?
Same with salvation. LDS theology doesn't merely say "we define salvation differently for ourselves." Doesn't it teach no onee can return to God's presence without accepting the restored gospel, whether it is in this life or in spirit world? This is a global claim that applies to Catholics, Protestants, Muslims, Buddhist, Atheist s, really everyone.
LDS interpret the fate of all humanity through uniquely LDS categories and in my opinion not Christian categories.
I'm not saying this makes Mormonism uniquely evil or dishonest because many religions make universal truth claims. But shouldn't we at least be honest about what is happening? You cannot say "your definitions are internal" and insist that everyone everywhere ultimately must conform to those definitions to reach God.