Aside from higher peak brightness I would assume it's also less prone to burn-in, the rate that OLED pixels degrade is proportional to how bright they run, and

Aside from higher peak brightness I would assume it's also less prone to burn-in, the rate that OLED pixels degrade is proportional to how bright they run, and distributing the brightness over two stacked layers means each layer only needs to run roughly half as bright. Not exactly half since the top layer won't be perfectly transparent, but close enough.