Personally I believe the Elementals to be Nymian "High Grand Mage" SCH egi gone rouge from the Magi-war & thus Masterless. Plus being in a pema-summoned state for so long & baring a deep grudge for Aether misuse as it maybe their reason they origionally rebealed, lead to their harsh treatment of "outsiders" as they claimed all the Forest their home especially mage-type ones, like those fleeing the fall of Ampodor who maybe Gridania's ansestors (or they got "tainted" during the war, thus turning them on their Master's like a Rampant AI with a virus, the great flood calamity could have even been a cause)... okay I might be grasping at crazy idea's there
As for Sprite's I agree their just passive naturly built aether entites that defend themself when threatened or gone mad (like when u posion, but not enouf to kill, a RL animal it kinda goes feral attacking anything it deams a threat even nearby "ally" animals). Sprite's may even be nature's way of saying their to much of "that element" missing/around & their there to be nature re-balance tool
Primal's are "thought givin form" with prayer & enouf "unused" aether (I say un-used cause I have yet to see someone use a high aether filled living Sprite as a mana sorce for Primal summon... which would be quite annoying if u could). Thou all are "Aether-made" its more a "How u make it" then a "what u made it with" rule for FF14... thou the thought of a boss using the Aether from defeated Sprite's to fuel a Primal/Arcane-egi summon does sound interesting in concept