13children born not of natural descent, nor of human decision or a husband’s [G435] will, but born of God.
Thayer's Greek Lexicon
STRONGS NT 435: ἀνήρ
- with a reference to sex, and so to distinguish a man from a woman; either
a. as a male: Acts 8:12; Acts 17:12; 1 Timothy 2:12; or
b. as a husband: Matthew 1:16; Mark 10:2; John 4:16ff; Romans 7:2ff; 1 Corinthians 7:2ff; Galatians 4:27; 1 Timothy 3:2, 12; Titus 1:6, etc.; a betrothed or future husband: Matthew 1:19; Revelation 21:2, etc.
The same Greek word is in
and Jacob the father of Joseph, the husband [G435] of Mary, and Mary was the mother of Jesus who is called the Messiah.
Here translating G435 as "husband" is clearly justified.
Now, let's get back to John 1:
12 Yet to all who did receive him, to those who believed in his name, he gave the right to become children of God— 13 children born not of natural descent, nor of human decision or a husband’s will, but born of God.
The first birth is of human decision. Denying that they became children of God through a physical act seems redundant. Indeed, as the OP states: since the physical act has already taken place. However, verse 13 is not talking about the first birth. It is not denying the first birth. It focuses on the second birth: born of God. It is saying that being born of God is not a decision of the husband.
It is a bit confusing, so I prefer English Standard Version:
who were born, not of blood nor of the will of the flesh nor of the will of man, but of God.
This brings out the contrast between (horizontal) man and (vertical) God much better.