When you talk about risk, you are missing the risk of the actions surrounding a murder, not just the act of killing itself.
"Slow and methodical" is literally the opposite of "quick and low risk"
When you murder someone on the street, there is a high risk for witnesses, but your chances of being caught in the act are lower because you spend less time committing the murder. Your chances of being caught after the fact are high because you did not plan it out and wanted it to be quick to reduce your risk of being caught when you committed it.
If you premeditate a murder and plan to clean up to the point of leaving no trace, the actions disposing of the body, wiping fingerprints, and cleaning bloodstains are when your chances of being caught in the act increase because you are spending more time committing the crime. Cleaning up after a murder should not be easy because your "reward" for doing a good job is an extremely low chance of ever being caught.
You are right, this is MafiaRP. The server is what the players make it. Why would a mafia hitman waste time planning an elaborate murder and cleanup when they can just pop someone on the street and run off?
The PK system we have now is significantly more involved than what you might find elsewhere. Sure some of the ideas might be fun or interesting, but they are not going to add some missing element to PKs or change the way people do them like you seem to think. We are pretending to be mobsters on a Half Life 2 mod from 2005. Any amount of realism surrounding PKs we have now should be considered a blessing if you look back and see what the alternative is.