This wouldn't be an issue should Bahamut and Phoenix are not treated as special summons. Also, this wouldn't also be an issue if the pet management were not taken away from the job.

The formula was already there: you started off summoning Carbuncle, then learned to summon the Egi's... then the trances... Logical evolution of the job should've been being able to summon the primals as a trance of the Egis.. but no. EW SMN happened.