Well, that's a pretty simplistic statement. In fact, if the NAs had had M16 automatic weapons and enough ammo, with the Americans using muzzleloading rifles, my guess is that the Americans wouldn't have stood a chance in hell.
Even as it was in the American West, when the whites had repeating rifles and pistols, the natives weren't so easily conquered even when they used bows and arrows.
I think, though there's no proof of it, if the NA's of the American west had formed one cohesive group, with the goal of keeping the Americans east of the Mississippi River, they could have done it easily ...at least for a long time. But the natives were tribal, and small tribes at that. Even the great Cheyenne nation was a loosely held collection of smaller tribes that seldom had the same goals or values.
Baron Max