Aiyana Jones was killed while a SWAT team was apprehending a murder suspect. Her death was unrelated to drugs. SWAT and no-knock warrant misuse is a larger issue that would not be solved by ending the War on Drugs.
"These estimates suggest that gang-related homicides typically accounted for around 13 percent of all homicides annually."
Even accepting that all of your assumptions are true--that most gang homicides are about drugs, that the War on Drugs is responsible for the existence of gangs, and that ending it would eliminate all gang violence--homicide rates would still not "drop like crazy" in the absence of drug prohibition.
It's actually the opposite. Homicide rates began rising in the 60's and were already approaching their peak when the Controlled Substances Act was passed in 1970 and the War on Drugs declared in 1971. That chart is quite deceptive in labeling the entire increase with "New Drug Laws."
The War on Drugs has generally been an expensive failure, but it is not responsible for every single social ill imaginable.