The stunt as you worded it not only gives greater bonuses (+1 to three or more elements, rather than +1 to two elements), but also avoids the limits on specialization structuring and the Lore limit. For example:
Consider, for example a spellflinger character with fire, air, and spirit elements, Lore 2, the "Control is its own power" stunt, and 1 Refinement. The free spec is +1 fire power, the Refinement grants +1 fire power and +1 air power. The final bonuses are +3 fire power, +2 air power, and +1 spirit power, despite the limit of gaining no more than the character's Lore as a single bonus. In addition, the best a character who got a second Refinement instead of the stunt could do would be +2 fire power, +2 air power, and +1 spirit power, so the stunt nets an extra point of bonus, as well!
This becomes even more pronouced if the character chose to use the Refinement to add the water element. Now the stunted version of the character has +2 fire, +1 air, +1 spirit, and +1 water, while the dual Refinement character gets only +2 fire and +1 air -- two fewer bonuses.
In addition, if the character with the stunt also has Thaumaturgy, the stunt allows them to control more power per roll than a character without the stunt, and allows this for all themes/functions.
Given this, the stunt -- which is supposed to grant about two shifts of situational bonuses -- is granting way too many bonuses.