I suspect that intake of the Power is what actually determines strength of a Channeler. Thus Egwene can take in and hold xx amount of saidar without using it. However, as she creates weaves she begins an outflow of power and can thus continue to intake additional power because the flows are using the power she can thus continue to intake enough power to hvae each flow fully powered without actually drawing beyond her maximum potential. Thus she can weave 12 individual columns of fire that each have the same amount of power dedicated to them but could not weave a single column of fire of significantly more intensity.

The Channeler is essentially a conduit. The amount of power they can hold is dictated by their potential, but the skill of splitting allows them to direct power in a continuous flow from the source to each weave equally.