I don't think Optae have niche to fill. They do have Centurion leadership at a cheaper cost, but Centurions unlock more detachments-per-point.
It would've been interesting Optae were given access to the same Consul upgrades. Specialists who aren't necessarily commanders. Like, being a good sniper or medic doesn't necessarily make you are a good commander, like being a good salesman doesn't mean you'd make a good manager.