Ancient Mass Child Sacrifice in Peru May Be World's Largest

I don't think so. It's probably mostly down to what Jared Diamond describes - Guns, Germs, and Steel.

The occasional score of children and conquests slaughtered voluntarily is dwarfed by the numbers of natives that died from smallpox (f.e.).

The Spaniards allied themselves early with these would be victims, who therefore helped remove the numeric superiority the Aztecs would have otherwise enjoyed.

These allied tribes (see the Tlaxcala) then became a privilege class among the natives.

The guns, and the horses, obviously helped - but we're talking 4 orders of magnitude advantage if the Spaniards had not allied themselves with the locals. Even pandemics cannot erase that advantage (and they take time to spread)

abraham was willing.

For the early humans many things obvious to us now were simply not known. The idea of an omnipotent sun god who controls the seasons isn't a priori crazy or anything. Why would it be? The normalization of how the solar system works only seems rational now because it's been scientifically presented to us.

In that sense a prediction that some entity controls this phenomena isn't necessarily superstitious. It's a fine prediction. But how do we get from there, to sacrifice?

Well, if we don't understand the mechanism of action for how these systems work, we can still try to make inference on them using statistics. For example: Sacrifice someone, then observe if anything changes. Before anyone ever ran this experiment, it's not obvious it wouldn't work. It's only obvious to us now because (a) we know the mechanism of action has no plausible link to human sacrifice, and (b) because people ran the experiment before, and it didn't work.

At the time, however, the benefit to this working would be huge, and the cost to society as a whole relatively small. This type of proto-statistical experimentation is, I think, what eventually led humanity to its core discoveries. In that sense we can't retroactively say the experiments that didn't work were superstitious or irrational, but the ones that did work were clever. For example, much of modern medicine arose from vast amounts of superstition and random experimentation.

Words are tools. Which label is more descriptive in this context?

That might sound glib but we have plenty of evidence even in our time of parents killing their children or allowing others to kill their children to save them from prophesied doom.

"For many rites, the victim had such a quantity of prescribed duties that it is difficult to imagine how the accompanying festival would have progressed without some degree of compliance on the part of the victim. For instance, victims were expected to bless children, greet and cheer passers-by, hear people's petitions to the gods, visit people in their homes, give discourses and lead sacred songs, processions and dances." [1]

[1] https://en.wikipedia.org/wiki/Human_sacrifice_in_Aztec_cultu...

The two terms aren't mutually exclusive (though the latter refers to unlawful intentional killing, and that probably doesn't apply here accept by importing foreign moral codes as law.)

And, in any case, “sacrifice” is used for things destroyed as offerings to supernatural entities irrespective of their value outside of that purpose for the people destroying them.