BoD is not as old as the 5th century, it is as old as the Good Thief. Dogmas do not change.
If St. Gregory nαzιanzus was against it, it is St. Gregory who was wrong, not St. Augustine. Just as St. Thomas was wrong when he doubted Immaculate Conception of Mary.
St. Gregory says "I cannot see it." You bolded this. He is giving his personal opinion. He doesn't say "The Church doesn't teach it."
He personally cannot comprehend BoD and that is because he gets himself tangled in a specious argument, comparing someone who has the will to baptism with someone who has the will to murder. The difference is that in the former case, the baptism is conferred by GOD, while in the latter case, that of the potential murderer, he cannot be a murderer until HE HIMSELF carries out that crime. These are two totally opposed kinds of potentialities -- as opposed as the divine and the human.
Murder is not a sacrament of the Church and God is not its author. Those who misuse their free will are the only authors of murder. However, God IS the author of the sacrament of baptism, and if He wants He can be free with it. He can save someone who desires to be baptized just as He can make the apostles walk on water, change water into wine, turn stones into bread, pull sheep out of the ditch on Sunday, etc.
That is, He has the power to bend his own laws if He so chooses, as "With God, all things are possible." He gave the example of the Good Thief to us as a clear confirmation of this, and I cannot even fathom the contumacy or obstinacy of those who deny it to the point where they won't even go to CHURCH with those who believe in BoD. Do you think St. Gregory would have refused to go to Church with St. Augustine?
That being said, we are past the point where some believe and others don't. It is now a defined dogma. Catholic Martyr refuses to go to a priest, take communion, or confess, and the devil I believe has gripped his mind. He interprets various papal sayings about the necessity of baptism as denying baptism of desire, but they do not -- that is his literal-minded misreading. I am done with this Sisyphean debate; the quote from St. Augustine sealed it.
I will tell you, there have been moments where I flirted with Feeneyism because of him, because one area that he is right about is that the Church has been steadily infiltrated with liberals. But BoD is not one of their heresies nor do I believe that any heresy was taught prior to Vatican II.
Now I have to study "invincible ignorance" which still bothers me, because I don't yet understand it.