Should be a bit higher ... but it's limited to 15 W (5V with 3 A) as the manual says.
A full charge should be done from 0 in about 1,5 h. So it's not that far off. The RC is not charging as fast as the batteries.
The RC Pro for instance is charging at higher voltage, 12 V or 15 V but also needs 2 h or 1,5 h with higher A of course (roughly 3,7 A). So calculating from 5,000 mAh (at 7,2 V) it may use up to 55 W.
That's not necessary in the case of the smaller RC (5,200 mAh at 3,6 V), as 1,5 h most likely suffice for most people, makes the components cheaper and reduces stress, ie temperature, in higher input power.