That depends on what you call "justice".
Should every person who ever killed another person for ANY reason be put in jail for life? If this were the way we should look at it, we should all lock ourselves up. Because we are all responsible for somebody's death in some way or another, even if you have to use the 6-point-rule to do it.
Is drinking and driving stupid? Hell yes. Should everyone with a grade-school education know better? Damn right they should. But lots of people get drunk, and lots of people drive drunk, not all of them cause accidents. Fewer of those actually kill people.
Is running across the street stupid? Yes it is. Should everyone with a grade-school education know better? Damn right they should. But lots of people do it and lots of people get killed for it. The man he killed I'm certain was in no crosswalk. Should be have been sent to jail as well if he survived?
Lotts is in prison Stallworth is not for two important reasons besides money. Stallworth committed a crime of stupidity. He drove drunk, and for that stupidity, someone died. He did not go out wanting to kill someone, he did not go out targeting this man in particular. He even stuck around the crime-scene, very few hit+run drivers do that. In short, Stallworth was stupid and owned up to his crime.
Lotts is in prison because he killed his brother in cold blood. He did not have the assistance of alcohol to inhibit his thinking, he did not have a car to propel him at inhuman speeds. He and his brother were playing a friendly game, that Lotts decided to make into a deadly one. Lotts is in prison because he made the decision to escalate a situation into violence and he chose to murder his brother. It was not a "stupid mistake". Thinking you're sober enough to drive is a "stupid mistake". Stupid mistakes do not include "I think I'm going to go from playing a fun game with fake guns, to taking a real knife and stabbing my brother."
So, is it "justice" that the death of a man by a stupid mistake results in a lighter punishment than the death of a minor by a desire to kill? Yeah, I think it is.