If that is what the Packers believe then why are they afraid to trade him to an opponent?
IMO, the Packers should've:
a) Let the two compete for a starting spot.
b) If Favre lost the spot to Rodgers, trade him.
c) If Rodgers lost out to Favre, wait until next year or when Favre finally retires to start the Rodgers experiment. You do after all have Favre signed for 2 more years! Weren't you counting on him playing those years out when you signed him?
This would ensure the Packers would end up with the better QB. If they had to trade Favre to an NFC divisional opponent, at least they could feel safe in selecting the better QB after allowing both QB's to compete for the respective starting spot.