I think you also forgot how Nolan completely destroyed a planet in a matter of seconds.

I think thats it. You cannot indoctrinate someone properly about being a supreme race if the person doesnt have that power yet. If Mark had his powers earlier, Nolan would have gone on missions with him and shown him how fragile humans are compared to them and that it is no issue when some die. That way Mark would have become more numb to the violence. He also could say stuff like “on Viltrume, that would never have happend. We have the technology to save those people anf our people are far superior so it wouldnt have happend in the first place”.

Also, the younger you are, the easier it is to influence someone.

I am more confused by the one on the left wearing glasses. Arent Viltrumite genes so pure that his eyesight should be perfect? And it cant be for protection either cause even his eyeballs are durable. We saw that in the fight between Omniman and Immortal. He hurt him a bit but no serious damage.