The National Journal disproportionately excluded low-crime, pro-gun states such as Vermont, South Dakota, and Maine from its chart of homicide rates precisely because their homicide rate was low. These states have few gun laws (Vermont has the least of any state) and very low homicide rates. If you disproportionately exclude unregulated states that are safest from the calculation of which states have the lowest homicide rates, that will create the false impression that states with the most gun laws have the fewest gun deaths.
The “pro-gun” states that consistently have higher “gun-related homicide” rates – such as Louisiana and South Carolina — have higher violent crime rates of all kinds, not just homicides or gun-related homicides. So it does not appear to be related to their gun laws. (For example, Louisiana and South Carolina have higher rates of non-gun-related homicide as well).