It would depend on the heatsinking solution though. Copper heatpipes for more efficient transfer of heat away from the LED, and more fins/surface area to dissipate that heat would theoretically mean a higher stable output than a solid chunk of copper with a small number of thick fins.
I wonder about using a design like the NoFan CR-95C CPU heatsink as a flashlight head. Flip the orientation of the CPU block, add gaps for the electrical, mount the MCPCB, LED, and reflector on the inside. Then add structural support with horizontal aluminum fins and aluminum posts. Waterproof or economical? Not in the slightest. The cooling potential should be excellent, though. Some napkin math says a single XHP70.2 cooled in such a manner (assuming some airflow and quality direct thermal path MCPCB) could theoretically sustain more than Caleb’s mentioned 5k lumens.
More practically, I doubt copper heatpipes would be economical, and thin aluminum fins flatly wouldn’t be sturdy enough. Maybe a vertical orientation of medium thickness, more densely packed fins, curved to provide better airflow when the flashlight is held parallel to the ground, attached to a copper heatsink would be an effective next step? It would be a unique look, at least.