You are right there is a contradiction between claims that the text has been transmitted accurately and the claim that the divine name stood in the original. So what? We’re not here to defend the JW position on every point. Let the evidence fall where it may. For my money the evidence is strong that the divine name was in the original text and was replaced in the second century. If that means the text has not been faithfully preserved, then so be it. A number of scholars have come to the conclusion that the divine name was in the original New Testament and give compelling and, in fact, very interesting reasons supporting that view. The lack of curiosity to explore this discovery, as Lloyd Gaston says, is striking in its neglect.
Can we quit talking about shadowy conspiracies? That is empty rhetoric. The fact is that the divine name was in the Septuagint in the first century but Christians replaced it with “Lord” when they transmitted the text from the second century onwards. Those who argue for the divine name in the original New Testament simply point out that the exact same thing happened in the New Testament that we know happened with Septuagint. There is nothing extraordinary or mysterious about it. If we know that something happened on Monday then it rings hollow to say it’s a wild conspiracy theory that anyone should suggest the same thing happened on Tuesday.