I went to Catholic school before Vatican II, earlier than each of you I'll wager. I never, ever, heard that the only way to Christ was through Panagia. I also never heard such a thing in Orthodoxy save the comment by +Gregory Palamas. I respect his opinion; it may theolougemma (I doubt even that) but it is not by any means the dogma or doctrine of the Orthodox Church. As for Fr. Meyendorf, well I guess he has his opinions, but they are nothing more than that.
As for the feast you mentioned, HC, it must be some sort of VII innovation, either that or the Irish Sisters of Mercy didn't celebrate it; May Crowning, yes. I even remember parts of the hymn we used to sing at it. It was quite nice. To the best of my knowledge, at least in the 80s when I was president of the local school board for one of the Roman Catholic parishes, neither the feast you mention nor the May Crowning were celebrated then.
Actually, it was established before Vatican II.
Especially when it comes to St. Gregory Palamas. Even if someone is not a fan of Fr. John Romanides, it is an interesting exercise to read Fr. Meyendorf on Palamas, and then read Fr. Romanides' two devastating review-essays that were published originally in the Greek Orthodox Theological Review (Holy Cross Seminary). A major difference between Meyendorf and Romanides is that the former was educated in the cerebral Paris school and had little or no contact with real monasticism, whereas the latter always remained connected with Greek monastic life.
I certainly am in no position to pass judgment on either scholar, rank amateur that I am, but Fr. Romanides seems to "get" St. Gregory and the thinking of the Greek monastic tradition: