I get your point, that there is a tension between the competing claims that the NT was accurately preserved on the one hand, and that the divine name has been removed on the other. That makes a certain amount of sense and is a viable criticism from a faith perspective. It is a well known problem that JWs have never directly addressed in the Watchtower.
Purely as a matter history, however, theological considerations don’t detract from the historical reasons for thinking that the original NT contained the divine name. 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.
I do think there is also a religious defence JWs could make, although they do not do so explicitly. They could argue that in general the NT text was preserved while the divine name in particular was removed, perhaps partly under the influence of Satan. But that Jehovah has played a hand in restoring the divine name in the last days by preserving crucial LXX fragments with his name and by bring in these to the attention of his named people Jehovah's Witnesses, who restored the divine name to the NT.