i don't think a street gang is even comparable with the mafia, the street gangs can't last more than 10 years at most cosa nostra is around for centuries
street gangs are involved only in drug and robberies, nothing else they have no future
nobody really took over, in some cities lcn disappeared coz rico law they don't really care of street gangs members
and where it is still strongly present it's by far stronger than any local gang