Two issues here: (1) Closely related animals (horses versus zebras) can differ widely in temperate. We can't assume that the llama species we've never encountered would be similar in temperament to the ones that survived. That's unknowable. (2) The earliest Mound-building cultures in Louisiana were almost certainly not agricultural. There were a few places in the world where conditions were favorable enough that populations could grow large enough to support monumental building. The key isn't agriculture versus non-agriculture. It's ability to have either stable or store-able food sources sufficient to support a large population. That can, in a few favorable places come from intensive gathering of wild grain and from intensive use of aquatic resources.
I agree with you regarding animal temperament. Camels and llamas have very different temperaments, which is why they tried to cross them in the first place...to get a nicer camel. Since most surviving members of the camelid family have been domesticated, Dromedaries, Bactrian camels, llamas, alpacas, etc. I don't think it is out of the question that extinct varieties may have had a suitable temperament as well. Of course that can't by guaranteed.
The whole purpose of a POD is to consider WI _____ were the case, WI _____ happened, WI ____ survived, died, was taller, was shorter, had never been born.
Regarding Watson Brake and agriculture...mea culpa, mea culpa, mea maxima culpa! You are absolutely correct.
"The new investigation, led by Joe W. Saunders of Northeast Louisiana University, indicates that Watson Brake may have been used as a base by mobile hunter-gatherers from summer through fall. Located above wetlands, the site would have provided access to vast aquatic resources during certain seasons. Bones of the freshwater drum, a species of fish that spawns from spring to early summer, and charred seeds of plants that ripen in the summer and fall were recovered at the site. The findings contradict the commonly held belief that major building projects took place only in complex societies with permanent villages supported by agriculture or trade. Mobile hunter-gatherers, it was thought, were unable to undertake such projects."