I agree that the last word of Rev 16:17, Γέγονεν (Gegonen) might be much better translated, "It has happened!" or similar (rather than "It is finished/done".) That is, I object to "It is finished" for the following reasons:
- There is much more that happens under the seventh bowl-plague.
- There is nothing finished or complete at the beginning of the seventh bowl-plague as far as Babylon is concerned
Rather, V17 appears to be a comment about what has just "happened" in V16, the assembly of "the kings [of the earth V14] in the place that in Hebrew is called Armageddon." This is probably due, in God's providence" to the natural outworking of evil to ultimately destroy itself. Note that the battle of Armageddon is not described here but is described in subsequent chapters.
I note particularly, that the "kings of the earth" will turn on the great prostitute, Babylon to destroy her (Rev 17:16, 17).
While God's complete foreknowledge means he knows/knew this, it is still a declaration when the alliance that creates Babylon splits into three parts (Rev 16:19). The preparation for the battle of Armageddon is the key event that sets this in motion. That is, the three beasts (Rev 16:13) assembling the kings of the earth is an act of defiance that is against their own interests, and that results in the destruction of Babylon.
Understood this, God simply declares something equivalent to: "They have actually been and gone and done it - they are crazy - they will destroy themselves." Or, more succinctly, "It has happened!"