1. Of course the pre-existance of Jesus feels much more real with a "he", but the KJV hardly inspired a generation of unitarian theology because of its "this one" back in the early 16th century.
2. Unitarians do not have an issue with poetic personification. Their clearest example of this, they would say, is found in the feminine personification of Wisdom in Proverbs 8. Yes she really is a she!
3. The word translated as "he", Οὗτος, is - I do not think it can be disputed - most commonly translated this or this one. Since it can also be translated "it", and "she", as well as "he", we still need to be careful not to overstate the pre-existent (male) Jesus.
4. Of the four tranlsations I checked in French, all state "elle" [she] and not "il" [he], because the Greek is so clearly referring to the LOGOS, which in French is the feminine word Parole.
My conclusion is that the "he" emphasis is a clear overstatement in English that both the Greek and the French bring us back to the author's intention, to restate the one in question is the word.