The book of Daniel appears to view the 4th Beast as the Roman Empire, which does look similar to the Beast in the book of Revelation. You are conflating the two, however. The Beast that Daniel saw was viewed from its point of origin, whereas the Beast that John saw was viewed in its last days perspective.It's not necessarily the Holy Spirit, but it can't be the Roman Empire either. Roman Empire was the beast from the sea with a lion's mouth, leopard's body and bear's feet, a patchwork of the previous empires; it receives a deadly wound on the head, but with the help of the beast from the earth, it rises again, and all nations on earth will yield their power and authority to it, eventually it would be like a re-enactment of the tower of babel. This would be the new Roman Empire, and it's more like the restrainEE than the retrainer.
So I would say that the 4th Beast from its origins, as Daniel saw it, was in fact the Roman Empire. And from the way John saw it, from its last days perspective, it is a European Empire under Antichrist.
The existence of prototypical Antichrists does not prove that the Restrainer is viewed, by Paul, as the Holy Spirit. Again, Paul inferred that the Restrainer was already understood by his readers.I trust the bible translators, and I do believe the restrainer is the Holy Spirit, at least it's the rule of law that keeps society in order. In the past several hundred years of history, you have Napoleon, Hitler, Musoulini, Franco, Stalin, Mao, all these are prototypes of the final Antichrist, and they were all results of violent civil unrest where law and order were removed, and I'm afraid this kind of history is repeating itself in America. In the end, this would be staged and replayed on a global scale.
This suggests to me that Paul is deliberately hiding the identity of the Restrainer. And this would make sense if he was insinuating, from the knowledge of Daniel 7, that the 4th Kingdom was the Restrainer, or the Roman Empire.
Paul would not have wanted the Romans to read his letter and hear that he was identifying the Roman Empire as something hated in the Scriptures and in his theology. So Paul likely hid the fact that the Restrainer was the 4th Empire in its unified state, awaiting ultimate fulfillment in the Antichristian Empire once that Empire had fragmented into 10 nations.