I also find it interesting that new scholars do not see the use of monogenes in Aeschylus (yes, it is there) as meaning "only begotten" not "one and only" as of any weight with respect to what the Greek means.
That's right; I'd forgotten about studies in the secular use of the word. But it's also significant that they can't account for why Greek speaking fathers understood it this way.
For a detailed analysis from an exegetical point of view, Geerhardus Vos' Self-Disclosure of Jesus, pp. 215ff. is satisfactory. He weighs up both sides of the argument, and shows that monogenes can only be confined to a temporal state because that is the perspective of the writer, and that it must refer to an eternal state in order for the various statements of the apsotle John to have their proper force.
Yes, I have made that point before to others - that Greek speaking fathers would be a much better place to understand a Greek word than men 2000 years removed.