Are you implying that after the Italian mafia there were no more organised crime gangs in the US? There's a huge number of organised crime gangs nowadays; who do you think is distributing the drugs responsible for America's massive drug problem? https://en.wikipedia.org/wiki/List_of_gangs_in_the_United_St... . A policy isn't a success if it kills one crime group only for it to be replaced with more, and the overall drug consumption/distribution rate doesn't decrease. More people are using illicit drugs than ever before: https://www.ibanet.org/unodc-report-drug-use-increase
You could certainly argue that RICO was too powerful and is often misapplied, but I've never before seen anyone argue that it has been ineffective.