I think the major difference is that a microcontroller can rapidly enter and leave sleep mode, and will likely spend most of its time sleeping. The other Pi pro

I think the major difference is that a microcontroller can rapidly enter and leave sleep mode, and will likely spend most of its time sleeping. The other Pi products do not support sleeping at all to my knowledge, which makes them an awful fit for battery powered devices. A microcontroller like this should be able to sleep for microseconds at a time or possibly even less (but you can obviously sleep for long periods of time too), letting you spend the majority of every second asleep, just waking up for brief instants throughout the second (possibly thousands of times) to do work. This enables huge power savings over something like the Pi Zero. You can also run the microcontroller at a lower clock speed to save more power, if you don't need to run at maximum speed to get things done. I would be curious what process node this microcontroller is built on, because I completely understand why these numbers would be discouraging when the microcontroller is running at full tilt.