So the dev team lacked the imagination to make 6 Egis relevant without the elemental wheel?
Garuda- ranged piercing damage + piercing resist down
Ifrit- melee slashing damage + slashing resist down
Titan- melee blunt damage + blunt resist down
Ramuh- ranged blunt damage + magic resist down
Shiva- ranged slashing damage + evasion down
Leviathan- melee piercing damage + a strong dot.
Resist reductions already exist in the game so none of these would break the game. The choice of which Egi would mostly come down to whatever the party make up was and the summons pair up when in parties with multiple SMN. Thats just from 30 minutes of thinking on this, SE are more capable than i. Loldrg isn't an issue because the requirements for summoning aren't high in the first place.
The issue is that SE wants to run a skeleton crew on this game to make extra money/to focus on XV and a real SMN would require more development. Also Sch is an affliction mage with heals so they had to dump affliction spells on ACN and by extension SMN neither of which reference these spells in their lore; an experiment SE already admitted was a mistake.