Djeggnog, I am glad you are proficient in languages. Not all of us are. When there is doubt or misunderstanding of a word, then it is time to bring in the dictionaries, like in this case. Etymology would be handy in the case of the Aramaic, Hebrew, and Greek word, not so much the English equivalent. In addition, the NWT is an American Bible, translated in the US of A, thus my use of Webster. I would say it is very relevant, or did they use the wrong English word for Greek genea? You be the judge. I know for a fact that the new "generation" interpretation of the Society is unique and unparallelled in the literature. That means they have created a novel and new interpretation that should be added to the list of standard English interpretations (e.g., those by Webster) or even those used by the Oxford dictionary, if you prefer to use that one. If it is as straight forward as you say, why is it so difficult to understand?
Quick lesson on the beasts according to JW theology. Notice "the beast that ascends out of the abyss" cannot bet the same as "the beast out of the sea", two different beasts altogether. According to the Society these are the same (see my quotes and footnote from the Revelation Climax-book):
Beast that ascends out of the abyss
This is the beast that “was, but is not, and yet is destined to ascend out of the abyss” (of inactivity). After World War I it would start off as the League of Nations, disappearing in the clouds of World War II. Afterwards it would be resurrected as the United Nations (cf. Rev. 17:8, 11). This is the beast that would kill the two witnesses (Rev. 11:7-10). In the book of Daniel it would be given the title “the [ultimate] abomination causing desolation” (Dan. 8:13; 11:31). This beast stands in the place of God’s kingdom, therefore an abomination in God’s eyes (cf. Ps. 46:8, 9; 72:3, 7, 8; Is. 2:4; Mic. 4:3).
Beast that ascends out of the earth
This beast out of the earth, is called “the false prophet”, i.e., the Anglo-American world power (Rev. 13:11), the seventh head of the beast, as well as the seventh mountain or kingdom, according to Rev. 17:9. It misleads, enslaves, and “performs great signs, so that it should even make fire come down out of heaven to the earth in the sight of mankind”. Eventually it would be destroyed (cf. Rev. 13:13, 14, 16; 19:20; 20:10). See False prophet.
Beast that ascends out of the sea
This composite beast stands on the sand of the sea, meaning it originates from the sea of humankind, similar to Daniels’ four beasts. It has seven heads and ten horns. The seven heads point to Egypt, Assyria, Babylon, Medo-Persia, Greece, Rome, and the British Empire. It looks like a leopard, has the feet of a bear, and mouth of a lion. The dragon gives it its throne, power, and great authority. One of the heads, i.e., the British Empire, had a death-stroke, yet revived. Two World Wars would devastate its economy. Only after joining forces with the Americans, would it survive the onslaught of the King of the North (cf. Is. 57:20, 21; Dan. 7:2, 3; Rev. 13:1, 2; 17:15). See Beast that had the death-stroke.
Beast that had the death-stroke
In Daniel (7:8, 20) we read of a small horn unseating three horns. It would become big and speak “grandiose things”. The British Empire would humiliate Spain, France, and the Netherlands to become the dominant world power. Its Royal Navy would rule the waves. In Revelation it is part of a beast with seven heads and ten horns. One of the heads had a “death-stroke and yet revived”. The beast spoke “great things and blasphemies”. People followed it in admiration. Authority was given it by the Dragon, Satan the Devil (cf. Rev. 13:3, 4, 12, 14). Its economy would be devastated by two World Wars. However, it would be bailed out by the Americans, becoming part of the seventh mountain or kingdom, the Anglo-American Empire of Rev. 17:9.
False prophet
This beast from the earth is the Anglo-American world power (Rev. 13:11), the seventh head of the beast, as well as the seventh mountain or kingdom, according to Rev. 17:9. It misleads, enslaves, and “performs great signs, so that it should even make fire come down out of heaven to the earth in the sight of mankind” (cf. Rev. 13:13, 14, 16). See Beast out of the earth.