I kind of disagree here. Against the initial attacks by conquistadors, being able to use metal arrows or atlatl darts against horse barding, metal swords and halberds against chainmail etc. will allow the natives to fight against the conquistadors in a more even manner.
I really don't know about this. Powder arms didn't decisively help Congo. Steel didn't help the Omanis. Pizzarro's expedition was hardcore mercenary types, while Cortez mostly had sailors and volunteers backing a very small core of professional soldiers. Nonetheless both were able to win decisive victories where large numbers of men were involved. Alvarado could have perhaps failed when he struck out on his own until his opposition decided to stand and fight, and then he won.
A lot of it had to do with the tactical adaptations that went along with the military technology, and that learning process seems to always lag the simple acquisition of technology. Will your army collapse when your leadership is killed? Will your army always withdraw in the face of direct attack because most warriors are skirmishers and have been trained as skirmishers all their life? Will your army be able to sustain itself in the field for a long time politically and logistically if stalemated?
I have considered this since the last time this topic was brought up in another form on another thread, and here's what I'm leaning towards now:
BKW makes an excellent point in that the places that offered the most resistance were where people were sparse, economic incentives for conquest were low, and regular expeditions had to engage against guerrillas that targeted civilians and infrastructure instead of trying to defeat the enemy's core army.
Russia wasted (comparatively) lots of resources keeping Chukotka down. The Spanish found it hard going against the Mapuche and the Comanche. The conquest of the Canaries was pretty painful. Portugal couldn't force its way deep into Zimbabwe.
Remove an exploitable population that can provide food for the conquerors and conquest becomes much harder or at the very least less interesting.
The other alternative is to outnumber the invaders by a really huge factor (see Qing vs. Russia/Dutch, some of the coastal African kingdoms vs. Portuguese and French factories, Arakan vs. European mercenary outposts), then direct military action becomes possible. But that's when the disease comes into play.
In Asia, Europeans carried the same disease package as their opponents. In Africa the balance was firmly against them. In America, they have the advantage. So the whole "acquire modern weapons, outnumber significantly" strategy would have to be considered AFTER the disease takes its toll. Can there even be enough population for that in America? It's a genuine question: I don't know.