Yeah, the SMN would have Topaz Carby for tanking. His potency could be slightly improved if he was just unable to do what Titan-egi does, but I dont think that would be the case.
You'd have Emerald Carby (complete with his own version of Contagion) for dps, and Topaz Carby for a tank pet. They could even add a melee pet in the expansion if they wanted to.

Egi's would just be a thing you fight to unlock the summon spells. And something that evil SMN uses in the storyline.