Halcon:
Essentially any group or individual practicing and promoting witchcraft, sorcery, devil worshipping etc. All things practiced in ancient Babylon (the nation presumably used as the model for the one in Revelation).
Or is this too simple of an explanation?
It is no explanation at all. It is conspicuously vague, and where it is specific, it is factually incorrect.
Babylon was used as a metaphor for Rome because Babylon had previously destroyed Jerusalem, and Rome did something similar. (This also invalidates the separate claim that 'Babylon the Great' was Jerusalem, as Jerusalem had already been destroyed when Revelation was written.)
You attribute far too much significance to the use of the term 'pharmakeia', which Revelation does not give as the primary identifier of 'Babylon the Great', and is properly seen as a metaphor for Rome's influence over its client kingdoms.
Also, although the Babylonians were polytheists, their deities were viewed as more capricious rather than each being definitively 'good' or 'evil', and they didn't practice 'devil worship' (a later concept introduced via Persian Zoroastrianism). And although they (and the early Jews with their 'Urim and Thummim') practiced divination, it wasn't 'witchcraft'.