How is that "grey-filled"? There's murder and there's negligence, basically reflecting direct vs. indirect role in causing the death. Both scenarios consider intent to gauge the severity. So you have two knobs you can turn, but which cover the entirety of human-caused deaths.
This is not a "grey-filled" scenario in the least. In fact, it's probably one of the most accessible and clear-cut cases of the law being reducible to simple rules.
What's often not simple is fulfilling the standards of evidence required to know which rules to apply, ie. how much evidence is needed to establish mens rea? But that's not what you claimed. You claimed that you can't have simple, intelligible rules that cover many shades of grey.