This is not the perspective adopted by many contemporary Christians who, in practise, often seem ready to discard the OT.
Quite right. Mostly because of a misunderstanding of what the Jews thought and how they thought.
Keep in mind that when Gabriel appeared to Zachariah in the temple, the Jews had not had a heavenly manifestation, or rather, revelation, for some 400 years. Also, one of the reasons for the targumim was the fact that the Jews were undergoing an incredible transformation in both language and culture. The Romans were winning many of their hearts and minds; building roads, aqueducts, new sea roots to India and the Far East -- a move that all but killed the caravan frankincense trade. And just a few decades later, in fulfillment of prophecy, things suddenly became far worse as Jerusalem was sacked.
The Essenes hid up their Jewish records in the Dead Sea and only was discovered just a few years before the source you cite. Then, no one knew much about the Jews or early Christians. About the same time the Dead Sea Scrolls were found, the Coptic Christian library was found in Nag Hammadi and now it was time for the Christian scholars to panic. Now that we know so much more about Jewish views and expectations, and about Christian views, we realize we are still lost in the paperwork. The WTBTS teaches many things we now know are just plain wrong. Teachings like man having a spirit was an old Hebrew doctrine, not a Greek intervention. Anyway, I look forward to hearing your views.