As a concept deity, power correlates with that concept.
Theoretically, if there were a deity of the concept of nothingness, they might be so powerful as to be alarming, potentially even able to arm-wrestle with Aeo.
For the universe will ultimately move towards nothingness, and even deities cannot escape annihilation.
Aeo is no exception. He will one day perish along with the world he created, but that day will be infinitely delayed, perhaps to the point of transcending the very concept of time.
Of course, some believe that Aeo is eternal and immune to the prospect of becoming nothingness.
Back to the main point, alchemy isn't exactly a broad concept; it's merely the collective name for many kinds of techniques.
To put it bluntly, if all the alchemists in the world disappeared, it wouldn't cause much of an impact. The destruction of Alchemy City would merely cause some turbulence in other nations, nothing that would stop their operation.
