I never understand the “lack of animals to domesticate” angle. They did domesticate animals, such as the llama and alpaca.

More could have been domesticated and presumably would have been if the had more time to advance. It’s a shame giant sloths were killed off…

Cattle, oxen, horses, camels, mules, donkeys, etc. The animals that are capable of heavy labor at or exceeding human level weren't present in the Americas. Llama and alpaca are more useful for fiber and meat than labor. Buffalo might possibly be useful but they are too big, wide-ranging, and aggressive to be easily tamed and bred.