Laika you are quite correct, and this is an issue I have given some consideration. As far as I am aware the WT has never directly addressed the tension between the competing claims of accuracy and corruption in the NT text that you mention (and I have looked for it). I can only say my own thoughts along these lines.
I find it interesting that a major supporter of the Tetragram in the original NT, David Trobisch, has a very liberal view of the textual history of the NT. He argues that the current NT is the result of heavy revision in the second century, including the suggestion that whole sections, or even entire books, of the NT were added at a late stage by editors to provide unity to the collection. Interestingly, while he believes the divine name stood in the original NT documents, he argues that the second century edition of the NT is what scholarly translation should aspire to reproduce. Thus he suggests introducing a form of notation in English to imitate the nomina sacra rather than restoring the divine name to the text. A very interesting set of propositions when you think about it. His book is fascinating and deserves to be read in full. His argument for the divine name in the NT is only a small part of much broader argument for the production of the NT as a unified collection in the second century. But in order to accept his argument, as you point out, you need to accept that the text of the NT was altered in significant ways during the first century of its transmission. Personally I find his argument persuasive on historical, empirical and logical grounds. But it does pose problems for those who take a conservative position on the faithful transmission of the NT text.
From a faith point of view, I can only say that I don't think it's impossible to hold a liberal view of the text, while also regarding it as inspired, and that God's name is very important. How can all those hang together? Well the fact is that the Bible has been corrupted in significant ways at various times. Those who argue that the Alexandrian text is close to the original need to admit that the Byzantine text, which dominated the Christian textual tradition in many places for many centuries, was regarded as the word of God even though it involved significant corruption.
This is a fact of history you need to contend with as a believer whether you are liberal, conservative or in between. Why did God allow an inferior form of the text to dominate for so long, before allowing the purer original to surface and reassert itself in the last two centuries?
You could pose similar questions with regard to the divine name. And if you are a believer it is not difficult to discern Jehovah's hand in the surfacing of crucial evidence for the divine name in the last days and it's restoration to the NT text. To be clear this is not an argument I have heard JWs make, but I find it easy to imagine it's the sort of argument a believer could make in these circumstances. And with some force since the discovery of key evidence and the unfolding of God's name in the last days does appear providential.