Do we call both pilots "Co-pilot". I think that one is the pilot and one the co-pilot. Is that right? If so, which is "senior"? If the "pilot" is "senior", then don't we have a use of "co" which does not imply equality?
I think of the analogy of the relationship between the Father and the Son, which may set your Unitarian teeth on edge. But we say "Eternally begotten of the Father."
Those of us who have done some begetting frequently complain that the actual begetting part was all too momentary. And the usual begetting activity involves starting something up that wasn't there before. (And, BTW, nobody that I know of has any problem with "There was a time when the Theotokos did not exist.")
But still, bearing in mind the not very good reproductive biology of the age, we say the Son is begotten of the Father.
Bad analogy. It's what we got. This is theology, after all, not a crossword puzzle.
It could even be a great analogy in Heaven, and see then face to face, not through a glass, darkly. :D