Scotty: There were no massacres under his rule.
'Superior' is a notoriously fuzzy concept.
It is quite believable that a conqueror/despot of half of Earth considers savagery to be a 'superior' trait; one quite consistent with having refined manners, being highly intelligent and a casanova, etc.
Spock: And very little freedom.
McCoy: No wars until he was attacked.
*After Khan takes over the ship*
Khan: Nothing ever changes, except man. Your technical accomplishments? Improve a mechanical device and you may double productivity. But improve man and you gain a thousand fold. I am such a man. Join me. I'll treat you well. I need your training to operate a vessel this complex.
I'm not seeing the savage part. Maybe Spock Prime saw it when he described Khan like this.
Prime Spock: He will not hesitate to kill every last one of you.
Only when he's pushed into a corner with no chance to get what he wants. Heck, even when he had the opportunity to destroy the Enterprise completely in The Wrath of Khan, he does something worse than hesitate. He gloats.
Khan: I deprive your ship of power and when I swing around I mean to deprive you of your life. But I wanted you to know first who it was who had beaten you.
And in a total savage like manner, is open to terms with Kirk in sparring his crew in exchange for Kirk and the Genesis information. Sure it might be a trick, but than again Khan could have easily killed the entire crew of the Reliant. But we can't have a Khan who could potentially be a good guy in this new take, can we? Let's throw in a heaping dose of retcon.
Jesus Khan: Spock, give me my crew.
NuSpock: What will you do when you get them?
Jesus Khan: Continue the work we were doing before we were banished.
NuSpock: Which as I understand it involves the mass genocide of any being you find to be less than superior.
Khan wasn't Banished, he fled. He didn't want to kill everyone he deemed inferior, only to give them his idea of order. He wasn't condemned to space as war criminals, he and his followers followed him to seek out a new world and build an empire without the interference of humanity. Nobody on the high court gave two craps about Khan's character outside of the fact that he was the villain in the film that's been praised to be the best film of the series. To them, Khan being the villain meant he was an inherently evil person which I is, as Jarod said, is Bull.