Well, seeing as none of those churches has an army, or a single tank, jet fighter, aircraft carrier or nuclear warhead, I can’t really agree with your assessment. They may be influential, but they aren’t really powerful.
Well, the chapter says it is more than influential, it says that the whore “rules over the kings of the earth”. The only way I can read that, in context with the revelation that the whore is a city, is to believe that the whore will be a city that is effectively the capitol of a world empire, which rules over all nations.
Daniel tells us that the “prince that will come”, who causes the “abomination of desolation” will do so in Jerusalem. This was confirmed by Christ in the Olivet discourse, specifically referring to Daniel’s prophecy. Then, John tells us in Revelation that the “great city” is where the Lord was crucified, and there is only one city described as “great” in that entire book (”Babylon the Great”). Then we are told that this whore, who has “Babylon the Great” written on her forehead, is a city, and that this city is accountable for the blood of the saints and prophets. We also have Jesus telling the Pharisees of Jerusalem that they are accountable for the blood of the prophets.
This is too many connections, explicit ones at that, for us to be searching around for other candidates. The whore, “Babylon the Great”, is Jerusalem, specifically apostate Jerusalem, whose people disobey God and reject Jesus until his final return. In Jeremiah 3, God speaks of both Israel and Judah as adulterous “harlots” whom he has written a bill of divorce. So, this is not new symbolism that the Jews of John’s day would have wondered about. They would have recognized those terms instantly as applying only to those who were once faithful to God, but had committed “spiritual adultery” by going after other gods.