when it comes to power, low end chips win by order of magnitudes ( for example http://ww1.microchip.com/downloads/en/DeviceDoc/30009941G.pd... ). But it all depends on what your power constraints really are

flash/RAM == size, cost, and power

Look at a die microphotograph of an ARM Cortex M4.

The RAM takes up more than half the die area. Flash is about a third of the die area. ALL the functional units and processing cores takes up less than 1/4 of the die area.

Very good point. For IoT widgets and perhaps even wearables, I'd rank things by power, size and cost coming in a bit later. The old way had cost first but people are seeing the light.