The dragon, the devil, satan that is written about in Revelation 12 is not a fallen angel, the dragon is Rome
Rev 12:3 And there appeared another sign in heaven: & behold a great red dragon, having 7 heads & 10 horns & 7 diadems on his heads
Rev 12:9 And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him.
The dragon is Rome, those who were in power who were not of God were cast out of heaven, the ungodly rulers fell from power, that is the meaning of “heaven” in Rev 12:7-8, just as it is the meaning of “heaven” in Isaiah 14:12, in reference to the man (Isaiah 14:16) named Lucifer who fell from heaven (power).
The Greek word “oikoumene” for the words “whole world” in Rev 12:9 are in reference to the “Roman world”, not the whole planet.