Of course it was only in the story because the plot needed it! Most things are only in a story because the plot needs it! And there was plenty of setup for it beforehand–an entire book’s worth in fact.

The fact that it was introduced and then never used again even though it is obviously unbelievably useful and apparently available enough that a 13 year old was lent one to attend extra classes definitely deserves some criticism but at some point you kinda just have to make peace with the fact that it’s a kid’s book and it’s really not that big of a deal.

You’re really doing nothing to dispel (no pun intended) my suspicions that Sanderson readers can’t understand anything that isn’t explicitly explained to them.