Extract the most restrictive cities (with their severe gang problems) and the US has one of the lowest firearm homicide rates in the world.
Help me out here, because I honestly don't understand the argument. The five cities in the US with the highest violent crime rates are, in descending order: Detroit, St. Louis, Oakland, Memphis, and Birmingham (AL). Which of these are "restrictive" by your criteria, and compared to what?
Note that I'm not actually making the argument that the US has a high firearm homicide rate (although it does among stable democracies). However, it's also worth pointing out that the US has ne of the highest firearm suicide rates in the world. Statistically speaking, if you own a gun, the person most likely to be killed by it is you.