AI Conquest is good enough. It can use loadouts I want to use competently and survive. I prefer it over Onslaught because Conquest is more mobile and Locusts last significantly longer than quad Annihilators.
AI Odyssey, at least the plasma cannon loadout I would use if I pilot it, has a death wish. It burns into a mob just like Onslaught would, then dies faster because of weaker defenses. Only if I give it beams and missiles, and maybe autopulse in the rear large, that AI hangs back far enough for its system to not be a suicide move, but such loadouts have less firepower than I want. I would have less problem with Odyssey if AI was not so suicidally stupid with plasma burn and short-range weapons (like plasma cannons). Also, even if I use plasma cannons on Odyssey, I need to leave most mounts empty (including the large synergy) to have enough flux to power two plasma cannons for a while and brawl like a battleship, and it is almost as stupid as unarmed carriers.
Also, I would say current unstable injector is closer to useless than niche.
It is niche. Great for Harbinger (it needs either Unstable Injector or x4 time shift to be fast enough to outflank enemies), and great for Reaper Afflictor (unfair glass sword wielded by player to assassinate key targets).
Also, Harbinger's Quantum Disruptor has annoyingly short range. Longer shot range is not very useful if Harbinger cannot drop enemy shields because QD has less range than the guns.