The scholars who argue that the original NT contained the divine name have various faith backgrounds that don’t seem to impinge on the matter one way or another. George Howard, Lloyd Gaston, David Trobisch and others argue for the divine name in the divine name in the original NT on historical rather than religious grounds. They would probably agree that the text has been corrupted in various ways because they are not committed to upholding the overall integrity of the NT text.
Whether your position is right or it is wrong, the Witnesses lose.
If your position is right, then there is absolutely no basis at all to believe any word in the entire Bible. The NT was promptly and so thoroughly corrupted that a central point of belief, the nature of God, was changed and forever changed the history of the church.
5000 manuscripts, the most well attested of ancient texts... means nothing. It still was corrupted within 50 years.
If your position is wrong, then the Witnesses changed the Bible to fit their ideology, and are therefore condemned by the Bible itself.
From a purely historical viewpoint, and given the historical evidence available to us, I think that the NT autographs did NOT contain the Tetragrammaton.
Up till 2018 when it was finally published and analyzed, there were tantalizing news of a possible First Century Mark.
Then it was published and lo and behold, it had Nomina Sacra. And it was 3rd Century.
If it had been 1st century, the Watchtower would have probably then argued that we need more 1st Century manuscripts to confirm either way, whereas 99.9% of NT textual critics would have said "This pretty much clinches it. It shows that the Tetragrammaton was never there."
They have been moving the goalposts since the 1980's...
In the 1980's the corruption happened in the 4th century.
In the October 2018 JW Broadcasting, they said that we needed 1st century manuscripts to prove this either way.