It is not about firepower. The Mexican army and marines have more than enough resources to kill the Cartel leaders. Almost, every time they have met the Mexican military wins. The problem is finding the leaders. It took 10 years for the U.S to kill Osama bin Laden, because it was hard to find him. The cartel leaders do the same, they are always in the run, it is believed that El Chapo lives in the mountains.

So far, they have captured or killed 24 out of the 37 most wanted drug lords.

http://en.wikipedia.org/wiki/List_of_Mexicos_37_most-wanted_...