Per the kW vs kWh, see top level reply.

Yeah a metric would be nice but it would need a standard test. That's why idle time and video playback time makes a good amount of sense. But it's not entirely clear how that would translate into usage for example in back country (where cell network drains power harder) or travel. So it's not perfect. But it is probably the best measure guven hardware and usage vatiation. In any case it's subject to marketing dudging the numbers in various ways.