Since I haven't seen where Fullness of the Gentiles has addressed this yet, in the meantime I will show how I might answer what you asked, which may or may not be the same way Fullness of the Gentiles might answer it.
Here's the gist of what I believe regarding Revelation 13 and 17's beasts:
Bearing in mind that the Bible is always consistent with its own symbolism, in the Bible we find the following symbols:
Serpent/Dragon: Satan.
Beast: Kingdom/empire/realm of authority, as in Daniel ch. 7.
Crowns: symbols of kingship, authority.
Horns: Kings/those with authority over whole nations of people, as in Daniel ch. 7.
Heads: The seat of a king/Capital cities of kingdoms, as in Daniel ch. 7 and Isaiah 7:8.
In the Revelation, which is packed with symbolism, we see the following:
* Revelation ch. 12's dragon has seven heads and ten horns, and
each head has a crown on it.
* In Revelation ch. 17 each of the seven heads of the beast
has a king (In Revelation 12 the dragon's seven heads each has a crown on it).
John was told the following about the beast with seven heads and ten horns in Revelation ch. 17:
"And the
ten horns which you saw are ten kings, who have received no kingdom yet, but will receive authority as kings one hour with the beast. These have one mind, and they will give their power and authority to the beast." Revelation 17:12-13.
* In Revelation 13
the dragon gives the beast ascended out of the sea its seat, its power and great authority -
and now there are ten crowns on the ten horns.
* Chapter 13 says the beast with its ten horns (which now has
ten crowns on its horns) will be controlled by Satan, and chapter 17 says
it will ascend from out of the abyss. So truly, this seems to be telling us about the same beast, because the beast that ascends from out of the abyss is controlled by Satan, whom the Revelation elsewhere calls the destroying king of the armies ascended from out of the abyss, and it has ten kings.
The three chapters (chapter 12, 13 & 17) when compared with one another most certainly seem to be talking about the same powers in the world, and one and the same final beast which is spoken about in chapter 13 and 17: These two chapters most certainly seem to be talking about
the same ten kings, and correspond with the ten kings of the final kingdom mentioned in the book of Daniel (Daniel ch. 7).
Therefore where Revelation 13 tells us that the beast will ascend out of the sea, this is just giving us more information about
the same beast that Revelation 17 says will ascend out of the abyss.
Same beast, same ten kings, some info on it given in chapter 13, with some more info given on it in chapter 17.
In the Revelation,
* Chapter 17 says that this beast will rise from the abyss and go to perdition; and
* Chapter 19 says it will be destroyed by Christ, along with its false prophet; and
* Chapter 17 says it will war against the Lamb and the Lamb will overcome it; and
* Chapter 16 says it will gather its armies for Armageddon; and
* Chapter 19 says that after overcoming it, Christ will throw it and its false prophet (mentioned also in chapter 13) into the lake of fire.
* Chapter 13 says that this beast
will make war with the saints and overcome them.
Regarding all of this prophetic scripture we are told, both in the book of Daniel chapters 7 & 12, and in the Revelation, that it's talking about the final kingdom in the world, which will consist of 10 kings + 1 king (or perhaps + 1 'kingdom'), because these ten kings will be united in purpose and be of one mind, and will hand over all their power and authority to another king/kingdom.
* Whereas Revelation 17 tells us that the ten kings will hand all their power & authority over to one king/kingdom, Revelation 13 tells us that a different beast (one that will rise from 'the earth') will exercise all the authority and power of the other beast (the one with the ten kings) in its presence, and while the other beast exists in the world.
* Unlike the beast with the ten horns/kings, this other beast (or 'kingdom'?) mentioned in Revelation ch. 13 will have
two horns like a lamb, yet it will speak like a
dragon, and will cause all those dwelling on the earth to erect an image to the seven-headed beast, and will cause all who will not worship the seven-headed beast or its image to be killed, and we are told that there is a number linked to the name of this seven-headed beast, which can be calculated: The number of this beast's name is the number of man (or of a man), and that number is 666.