Regarding the phrase "son of Mary" is one aspect of Jesus' relationship to her, and you might claim it also as a title. Regenerated believer-disciple-priests are also relationally children--sons and daughters (not capitalized in AV or DRB as proper nouns)--of The God, but only Jesus has the title "Son", given by The Father.
In Isaiah 7:14, 9:16, and capitalized as a proper noun in Mark 1:11, "Son" is a title, proclaimed by The God, and not merely a relationship term, as it is usually employed.
To firmly stamp this, Jesus became the Only Begotten Son, the only human Son flesh-begotten by The Father, as was Adam. He was not merely made in the image of Elohim, He Is Elohim, God With Us.
Son of Mary is acceptable to Muslims. Son of God is not. Their Allah had no son. Capisce?
(With reverence . . .)
Ohhh Kay.
Yeah, gotcha.