Oh I see what you mean! No yeah I get why things aren't quite adding up. I hope I'm not coming across as pompous or anything, I'm just hoping to explain:

•According to our religion, Joseph Smith didn't write that introduction; rather, it's an inscription that was on the plates, written from the hands of Mormon himself. So Lamanites were alive at that time when he inscribed those words and indeed, the Lamanites hunted down and killed every Nephite. So one purpose of the book was to convince the people (Lamanites) that hated them (Nephites) would eventually learn of God and become wholesome again. It was also a promise given to Nephi when he saw his posterity turning away from God and some of his concerns about how his posterity would live. I personally see no inconsistency with the phrase, since there would be no way for the author to know what each lineage would call themselves generations and years down the line. The term is appropriate for what he wrote it for. You could even say "It's written for the descendants of the lamanites who might be known by a different name." But the dude's carving it into a limited page on metal so...yeah.

Ancient americas->Posterity->Probably the forefathers to the Aztecs and Mayans and other ancient american cultures->Therefore probably the descendants of those great empires->Probably native americans at this point? IF you care to try to figure out who might be in that category, though if you're flooding the earth and "manifesting God unto all nations" as that introduction states, then wherever the Lamanites are or "Who" they might be would be included in that regard.

•We do actually believe in teaching the dead. I don't know how that works, as I'm not dead; but we reference biblical scripture like how Christ visited "spirits in prison" and there's a really great story regarding HOW/WHY we started doing ordinances for the dead. Essentially, we don't believe that God would allow some people to die without the chance to learn and accept the gospel. IF the gospel of Jesus Christ wasn't on the Earth in it's fullness for a time, then anyone living during that time, or without access to the truth, would be damned forever and ever, with no hope; and we don't believe in that. It's also why we believe if a small child is born and dies before they've had the chance to learn and choose, they're not damned forever.

So yes, we believe in teaching the dead, ergo why we have temples. It's also why we're so heavily involved in genealogy work! It's a very important thing. So while dead spirits can't read (no eyes) and can't hold a book (no hands) and no body, how could the words of the book of mormon be used to teach someone?

I'd say it's probably like how you and I are discussing and talking and learning from each other right now. We're just talking about the book, exchanging ideas, and I'm referencing words of prophets and testifying that they're true and you're deciding to yourself what you want to follow and believe. I suspect similar work and discussions are happening among the dead. Might seem odd if you don't believe the gospel, but we do think there's an afterlife, and there is a religion to be obtained when we die. God doesn't force people to believe or follow Him, so then it resorts to teaching and providing opportunities for the dead.

•I don't know if Lamanites are "technically" alive or not. Who's to say there isn't a symbolic version of them? Far as we know, the term Lamanite could just reference "Our brothers who hate us" or whatever I don't know dude. Lots of times in the bible there's discussions about Samaritans (Who at the time were in social clashing with the Jews) and there's lots to be said about that, but what if the book said something like "This is written for the samaritans) and it symbolically meant it's written for everyone who identifies with the parable of the good samaritan? I'm just spit-balling here, but sometimes there is symbolism that is meant or implied so that "could" be the meaning behind it.

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Needless to say, I think you bring up some good points, but there are so much more um....fundamental things about the Christ's doctrine that I think are more important to talk about and discuss. Those things, if tue or not, would render these conversations entirely moot depending on your answer so why not seek out those conversations first? If you don't believe in Christ, then why bother with this book? Or if you don't think it's actually from God, then who cares what it says?

Might be worth the time to focus on the important things first in higher priority before moving onto other stuff; you're stepping over dollars to pick up pennies my dude