The current 3V Pro models have buck drivers, they just don’t regulate very well as you discovered. You can achieve flat regulation with a very low Vf LED like the Nichia E21A, as well as swapping the leads to a more appropriate gauge and using a better 18350, but that’s more practical for the Tiara.
I would strongly suggest swapping the optic for something more appropriate since it looks like Armytek is still using the wrong one.