High temperature is the point. The efficiency of heat engines depend on the temperature difference (relative to ambient). The hotter you can go, the better. (granted this thing isn’t really an “engine”, but the trend still applies)

But for practical applications, the availability and cost of materials to survive the operating temperature is also relevant.

A Carnot heat engine operating between, say, 2600K and 400K can reach almost 85% efficiency.

The higher the temperature, the higher the share of exergy in the heat flux. At high enough temperatures, it’s no longer a feat to convert to electricity at high efficiencies.

It would be pretty hard to create a carnot heat engine that can withstand 2600k. I'm not even sure if for example Tungsten has structurally integrity at that point.

That might be when copper liquifies. It will lose its structural integrity and deform easily at much lower temperatures.

Pfff! Amateur! You should try pulling the plug out of the tub when its filled with my wife's bathwater.