In short, there were no beasts of burden in Mesoamerica, nor was the wheel used in transportation. This makes the description of horses and chariots completely anachronistic, unless you accept that Mormon originally wrote, "Now when Lamoni had heard this he caused that his servants should make ready his ceremonial battle beasts and his wheel-less litter."
There is no "record", yes...but obviously any talk of Llamas is not going to be sufficient for your cynicism, and likely not for my skepticism.
However, it would seem that you are implying a certain use for chariots from its significantly limited use in the Book of Mormon. I mean to say, why is the chariot not used with more frequency in the Book of Mormon? It plays a significant role in the Bible, but it is all but barely mentioned in the Book of Mormon, and those mentions are not truly conclusive as to what purpose the chariot served.
Not that your speculation is not applauded, but it is still speculation.
It is perfectly reasonable that horses existed but no remains have ever been found.
well, except horse bones were found at Mayapan, dating centuries before the Spaniards.
excavations from Cenote Ch'en Mul have also uncovered traces.
In short - The Tikal Palaces have imagery which clearly illustrates Kings going into battles upon a litter with protector beings all about. It is completely reasonable that Joseph Smith, upon translating, would encounter such an unfamiliar concept and convey the imagery as "horse and chariot" - which is pretty spot on.
but more importantly -
you fail to read the Book of Mormon
In Ether 9:19 we find,
And they also had horses, and asses, and there were elephants and cureloms and cumoms; all of which were useful unto man, and more especially the elephants and cureloms and cumoms
Now the Book of Mormon being a linear translation makes the jaredites hardly an afterthought when one considers Alma 37:21
all in all it would seem that you ignore the context, about how the story of the destroyed civilization to the north is an integral part of the Book of Mormon narrative.
But what about modern science? Science believes that horses, mammoths, etc. came over the land bridge but then the Pleistocene period ends and many "large animals" are believed to have gone extinct.
that being said, sounds like gnat-straining to me (bzzzzzzz)