I have to shake my head and laugh at some of the things you say...
The total number of gang members do not outnumber the total number of the US military or law enforcement.
There are approximately 700,000 gang members in the US.
There are approximately 1.2 million police officers in the US.
There are approximately 2 million members of the military in the US.
Now add in the retired members of both the military and law enforcement who are still capable of operating.
Yeah, gangs would die in droves.
The violent left would die in droves.
VERY few of those gang members have any sort of firearms or tactical skills. Most of them hate each other so most of them will not work together...for any reason.
Next point, see @NeuroTypical's comment above about AOC and Pelosi and gangs.