Joseph is His legal father. He was also the direct blood descendant per Matthew of David and all the preceding kings of Judah. Without him, Jesus would be a usurper to David's throne. He would have no more right to reign over the house of Jacob than Herod did.

He is still just a man. Mary is still just a woman. He was born in a sinner's womb. She was saved. That is hardly minimized to nothing. She can't save you. She couldn't die for your sins. Believing she does is silly. Jesus saved you because He loves you, not as a favor to mom.

[Luk 1:31-33 KJV] 31 And, behold, thou shalt conceive in thy womb, and bring forth a son, and shalt call his name JESUS.
32 He shall be great, and shall be called the Son of the Highest: and the Lord God shall give unto him the THRONE OF HIS FATHER DAVID:
33 And he SHALL REIGN OVER THE HOUSE OF JACOB FOR EVER; and of his kingdom there shall be no end.

[Mat 2:2 KJV] 2 Saying, Where is he that is born KING OF THE JEWS? for we have seen his star in the east, and are come to worship him.