Of course, the CPU/GPU of the X3 NFC (5W TDP) consumes significantly less power compared to the X3 Pro (10W TDP), which means that the Screen On Time is higher compared to the X3 Pro. A computer with a Core i3 CPU and a GTX 1650 Super also consumes less power than a Core i7 with a RTX 3060 Ti. You can of course undervolt the CPU/GPU of the X3 Pro, but you will probably never get the power consumption close to the X3 NFC. The cores architecture, clock rates, the internal memory and the memory bus + RAM speed used in both devices are also different, so that you can't really compare them.
The SD860 is about twice as fast as the SD732G (at least in synthetic gaming benchmarks), so it should be clear that this additional performance has to be bought with additional consumption somehow.