It's a nondoctrinal hypothesis whatever it's merits. I believe with regards to the Book of Mormon that a horse is a horse. Now a curelom or cumom? Sure. But I think Llama here.
If a horse is a horse, the problems are actually compounded, which is why so many apologists try to find an alternative.
Once again, I refer you to the essay on my website to get an idea of just how many problems you create with "a horse is a horse" theory. Apologists may be misguided, but they're generally not stupid. If a "horse is a horse" solved anything, don't you think they'd avoid the silly tapir argument to begin with?? They've actually picked the lesser of two evils.
http://www.mormonmesoamerica.com/horses.htm
(ps, there were no llamas in mesoamerica)