Either John (Scripture) is lying, or the Commentators are lying. And YOU believe the Commentators.
No, I am going with the Bible, not the commentary you posted that attributes what the angel said to John as being from John himself and fabricated by John so as to lend credence to it. So I don't care what that commentary says. Because it can't even see that John is relating the words of the angel speaking to him, not writing his own prophecy. Now if you want to share his pov as your own that's fine. We'll examine it in the light of scripture. But don't think it's somehow authoritative and accurate just because it's some kind of official commentary.
Here's the passage of scripture. The angel is speaking this prophecy, not John......
Revelation 17:7
7Then
the angel said to me: “Why are you astonished?
I will explain to you the mystery of the woman and of the beast she rides, which has the seven heads and ten horns.
8The beast, which you saw, once was, now is not, and yet will come up out of the Abyss and go to its destruction. The inhabitants of the earth whose names have not been written in the book of life from the creation of the world will be astonished when they see the beast, because it once was, now is not, and yet will come.
9“This calls for a mind with wisdom. The seven heads are seven hills on which the woman sits.
10They are also seven kings. Five have fallen, one is, the other has not yet come; but when he does come, he must remain for only a little while.
11The beast who once was, and now is not, is an eighth king. He belongs to the seven and is going to his destruction.
Now compare that to the commentary you posted and what Einstein, Frederick, and Lewis say who's speaking.....
“[The] five of whom are fallen [presumes John’s work to be written in] Vespasian’s reign. Titus is to come, but only to last for a short time.
Perhaps the writer knew of the hopeless condition of Titus’ health. He is therefore either using a literary convention, and assuming an earlier date than is the fact to give his words the force of a prophecy concerning Titus, or, more likely, his is using here material written in Vespasian’s reign which partly suits his purpose and partly not; for there are very good reasons for thinking that this book was written, not in Vespasian’s reign, but in Domitian’s.”
[1]
[1] Eiselen, Frederick, Edwin Lewis, & David Downey, The Abingdon Bible Commentary, Abingdon Press, NY, 1929, p. 1392
So, believe what you want about the timing of the kings existence, but please leave these clowns out of the discussion and we'll compare what you believe (wherever you got it from) to the scriptures and we'll have our own little discussion. If I was that angel I'd strike each one of them commentators dead, lol! "Using a literary convention", "assuming an earlier date than is the fact", "to give his words the force of a prophecy". Even an angel would be insulted by those accusations.