Steel armor was definitely a huge advantage and the Indians soon learned that the only two reliable ways to defeat armored soldiers were to drown them or to throw large stones at them if they ventured into a narrow valley. Neither was usually available.

"the Spanish were vastly outnumbered, so their weapons alone were irrelevant in the battle"

Irrelevant? Tell this to Atahualpa Inca, who, during the second big Spanish conquest, was taken alive by a group of mere 168 Spanish soldiers, unsupported by any local warriors, while having at least several thousand guards with him. Force ratio of 40 or 50 to 1 ultimately made no difference.