Show me your lunchbox!

On the other hand, consider what would have happened if Nexon hadn't given this person a lunchbox.

He would set out to create himself a perfect weapon. Let's assume he would spend the same 7B on clean swords and sword scrolls, and blow them up one after the other until he's got the godliest sword he could make. And he's use it himself, not sell it.
Net result: a large number of clean swords "removed from the economy", and all the scrolls used on them, and finally the godly sword which is also not "floating around" because the owner has no reason to sell it.

So is the lunchbox, saving all those swords and scrolls from untimely death, really a gold sink?

If Nexon hadn't introduced the LunchBox then you have a point. But they did so it's a moot point.

You could also consider what would happen if Nexon introduced yet another item that trumps the above godly sword. Let's say they introduce a lvl 140 1H sword with a 125 base atk.

Now the player has an incentive to sell it. You see with an untradeable item this can never happen. The lunchbox hero and the godly sword hero would both have incentive to get the new super dee super sword. The lunchbox hero would not have that 7B to use to upgrade to the next one. Those sunk mesos will remain just that.

The mesos that were previously used to murder all those poor swords will now make their way to some other player in the form a godly and tradeable sword.

Anyway, we could go on and on with different scenarios in a thread about lunchboxes. My point was that scrolling an untradeable item is at least a partial mesos sink even if you pay someone else for the scrolls.