“...Christ is the only one ever referred to in scripture as being full of grace ...”
See the bible Luke 1:28 and inform both the Angel Gabriel and St. Luke of this since they don’t seem to have gotten the memo.
From the category of “words mean things” - the expression “highly favored” does not equal “full of”.
Luke 1:28 - And the angel came in unto her, and said, Hail, thou that art highly favoured, the Lord is with thee: blessed art thou among women.
“Highly favored” - charito (khar-ee-to’-o)
highly favored From G5485; to grace, that is, indue with special honor: - make accepted, be highly favoured.
John 1:14 - And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth.
full - pleres (play’-race)
From G4130; replete, or covered over; by analogy complete: - full.
Mary was MADE acceptable by God’s grace. Christ IS the fullness of God’s grace (see the memo found at: Col. 1)
As to the angels understanding “the memo”, the scriptures bears out this record:
Rev 7:9 After this I beheld, and, lo, a great multitude, which no man could number, of all nations, and kindreds, and people, and tongues, stood before the throne, and before the Lamb, clothed with white robes, and palms in their hands;
Rev 7:10 And cried with a loud voice, saying, Salvation to our God which sitteth upon the throne, and unto the Lamb.
Rev 7:11 And all the angels stood round about the throne, and about the elders and the four beasts, and fell before the throne on their faces, and worshipped God,
Rev 7:12 Saying, Amen: Blessing, and glory, and wisdom, and thanksgiving, and honour, and power, and might, be unto our God for ever and ever. Amen.
Looks like the got they memo, all right.