With the 3000 mAh battery found in typical phones, @ 3.7 Volts, a power draw of 2 Watts would completely deplete it in 5.5 hours. 5 Watts would deplete it in 2.2 hours. 8 Watts would deplete it in 1.4 hours. So I'd say the 2 Watt figure is pretty accurate.
The nm figure used by different manufacturers are not comparable to each other. They are quite literally measuring different things when they deem a process to be x nm.
- Intel's 14nm process yields 37.5M transistors per mm^2
- TSMC's 10nm process yields 52.5M transistors/mm^2.
- Intel's 10nm process yields 101M transistors/mm^2.
- TSMC's 7nm process yields 114M transistors/mm^2
- Samsung's 5nm process is 126.5M transistors/mm^2 (although this is memory, so somewhat more compact).
- TSMC's 5nm process is projected to yield 171M transistors/mm^2
So Intel's 10nm process is actually more comparable to TSMC's 7nm, than to TSMC's 10nm.
The problem with comparing Geekbench scores across different CPU platforms is that several of the things which comprise the benchmark have hardware assist on some CPUs, not on others. This results in substantially higher scores on the CPUs with hardware acceleration. But the reason general purpose CPUs are missing hardware assist for these functions is because the task is extremely rare (like AES encryption/decryption), and the CPU is very fast. So it's not worth devoting the silicon to it, because in the rare instances where it's needed the CPU can complete it in a reasonable amount of time. But in something like a SoC, the general purpose part of the CPU is so slow that AES would completely cripple performance. So they have to add hardware AES encryption/decryption to make the SoC usable in the rare instances where it will be needed.
The benchmark does not weight these according to frequency of need as is done in the CPU design process. It weights these rarely-used functions the same as commonly-used functions, resulting in the hardware acceleration in SoCs exaggerating their benchmark score compared to general purpose CPUs. Whereas in real-world tasks, the general purpose CPUs dominate.