Rand grew in strength as a channeler throughout the series, but strength in the Power is probably related to your affinity to the Pattern in some way. That's why channelers like Egwene with a strong affinity are strong in all the Powers and can also summon weaves from nowhere (like the flame of Tar Valon).

After Rand's experience on dragonmount when he was truly transformed into the Creator's herald, he became the strongest man alive.... He could channel massive amounts of the Power. Egwene believed that the whole Tower would not hold him... He just can't be contained or controlled.

After TG he has gone to the next level... His affinity with the Pattern is total or perfect if you want to look at it like that. Now he can manipulate the Pattern with will alone. He's probably a bit like Neo from the Marrix who suddenly unlocked his abilities with each greater step of self awareness.