I am not making excuses for Bukele's heavy hand in gang violence but I live in one of the most dangerous cities in the world when it comes to murder and I can tell you there is no other way to deal with it under a fiat system
Once gangsterism takes hold its pretty hard to weed it out, even the heavy hand is only a temporary solution, it just further drives them underground and radicalises them. As long as the profit motive in gangsterism is a higher premium than you can get elsewhere these movements will keep growing