Why? The elemental spells all generate more mana than their equivalent balance spells, and it's only the base spells in the single target rotation that are ordered in the rotation from lowest to highest mana generated. The AoE and finisher spells are all used in order of lower dps/higher mana ---> higher dps/lower mana. It also makes sense to me that the balance spells are slightly less potent in terms of generating mana due to being generalist spells while the focused spells are more efficient at generating mana due to their focus.