Of course a pope, as it were, was not in existence during John's prophecy because his prophecy is about End of Days.
But John is being told that the beast was already in the bottomless pit in his day. The beast will become the 8th king, of which 5 had already fallen. With one existing at the time. And the seventh king future of John's time.
It is an advanced study, but the crowns on the heads and horns of the beast portrait in Revelation 17, Revelation 12, Revelation 13 are all different - because they are taken at different periods of time.
Revelation 17 - 1st century
Revelation 12 - with 7 years to go before Jesus's Second Coming
Revelation 13 - with 42 months to go before Jesus's Return
The popes, none of them fit, as any of the kings.
This is why you have to take it for what it is: popes were not rulers of anything until 1929, when they became their own nation-state, sovereign and all. Since then, there have been eight "kings/heads of states/rulers/etc. Francis is the eighth. So when John talks about a harlot that sits on seven hills, who has five kings fallen, one IS, and one is to come that will last a short while, he is having a vision during Pope John Paul II's reign as pope. Benedict XVI is the seventh (lasted only 8 years, first pope to "quit" since Gregory,) and the 8th that is of the seventh is Francis I. Francis is the first Jesuit Pope. The Jesuits are the army of the Church. They work for the commander in chief: the Pope. Francis is OF the seventh. His boss was/is Pope Benedict XVI.
John was not having a vision at all regarding the kings - he was being
told by the angel what the horns and heads were, and where the actual beast was - because John could not see into the bottomless pit,
Revelation 17:7 And the angel said unto me, Wherefore didst thou marvel?
I will tell thee the mystery of the woman, and of the beast that carrieth her, which hath the seven heads and ten horns.
And the angel said regarding the seven kings "one is", not in the future, but right then at the time of John.
The prophecy of the 7 kings was not complete in the first century, so there are no crowns on the heads in Revelation 17:3
In Revelation 12, with 7 years to go before Jesus Returns, the 7 heads have their crowns, indicating that the 7th king has come to power, the end times Antichrist person. Nothing to do with a pope.
In Revelation 13, with 42 months to go before Jesus Returns, the 7 heads don't have crowns indicating that the prophecy of the 7 kings is over, with one of the heads (the 7th), the Antichrist, mortally wounded and recovered.
The beast is visible to John in Revelation 13, because he has ascended out of the bottomless pit to possess the recovered Antichrist. John doesn't have to be told by an angel anything in Revelation 13. In Revelation 12 and 17, the actual beast is still in the bottomless pit, so what John sees is Satan the power behind the beast.
Doug