It’s not just in airplanes:
Co-stars are subordinate to the stars;
Co-conspirators are subordinate to the main conspirators;
Coadjutors are subordinate to suffragan bishops;
Co-dependents are subordinate to their dependents;
we could go on and on, but really there’s little point.
The language offends them, and they prize their offence over any attempts to explain or to provide context.
I would submit that is our Lord whom we prize, and that which He has given us. Your explanations fall upon deaf ears because they cannot be true. There is no context in which a 'co' of any kind will be sufficient. I will not suffer that credit being taken from Christ by even the least increment, subordinate or otherwise.
That Jesus died for me at Calvary shows His deep and abiding love for me personally. What need have I for any other? My Lord need not be wheedled nor convinced with regard to His concern for me and mine. We stand boldly before the Holy of Holies and simply ask. No "goddess of heaven", no angel, no saint, no "priest" gets credit for that. There is only one Redeemer. There is only one Mediator (Priest). One Savior is all I need.