You can make that general argument about any single approach to reform. Let's not put all our hopes in any one single solution, and let's not be misled into false dichotomies.
Structural issues which create gangs need to be addressed, and it's true that convicting the gang members might detract from the need for those structural reform, but enforcing laws is still a part of the incentive system we have to encourage people to not break the law.
We should fix structural issues, but that doesn't mean we need to leave clear bugs in tact to increase pressure on fixing those issues.