So...you were not yet racing, just killing some time?

And he wouldn't take the...30 seconds...to luff up so you could grind the new (stretched) halyard back up to where it should be?

Or do I misunderstand the situation?

To explain it to him, tell him not only are you moving the draft foreward when you pull the downhaul tight, you are also bending the mast, which pulls the draft out of the middle of the sail. The outhaul only flattens the foot area up to a certain point, but not very far up, maybe only the bottom 1/3 of the sail. To get the middle flatter and get the leach to open up (is it a square top?) you need to bend the mast, and you do that with a (very) tight downhaul.

We did this in J24's too (bent the mast to flatten the mid sail area), but we used the backstay to bend the mast. Most monohulls have an adjustable backstay to pull on which is more powerful than their cunninghams.

Does a Stilletto have an adjustable backstay?