An army of superzombies wasn't really the point for Necron.
The point was trolling heroes- Apparently Necron required intense emotional responses followed by death to get the most bang for his buck, or maybe he's just a massive troll.
Hence heroes getting visits from exes, siblings, children, parents, etc.
As powerful as a kryptonian black lantern is, Superman just isn't going to have an immense emotional response when confronted with his third cousin five times removed that he'd never freaking heard of, much less his father's college roommate's cousin's hairdresser.
So if Nekron revived a bunch of Burning Martians, it'd be to send them after the Guardians, they only people who remember them and hence might give a damn. If the Guardians have the emotional capacity to have an immense emotional response by such a confrontation.
Bad things by definition have to begin, otherwise no badness.