Yes. But that is my point. If humans and omnics/robots lived in peace, at what point would the omnics/robots realize that they are vastly superior to humans and that they don’t need the humans at all. There is no guarantee that wouldn’t happen and while a majority maybe might advocate for keeping humans around, I doubt most humans would want to live in fear of that.
Furthermore, would you want to have to accept that you, the beings that created something equal or greater to yourself is now at the whim of that very thing? Would you want to accept that the only reason you are allowed to exist is because of the kindness of a being that in no way is weaker than you? It would be disgusting. There would be divides, abuse, oppression, and other stuff that would come from allowing omnics/robots to exist peacefully with humans for an extended period of time.
This is the very concept that Overwatch as a narrative can tackle very loosely on seldom occasions.