The reason africans can be overstocked so easily is becuase they generally stay small, and have a live to fight another day attitude. Not to say they won't kill other fish, but it isn't anything like the lip locking fight to the death battle royale that CA and SA bruisers can engage in. Especially large ones, with no where to run, its almost sad.
In a LFS I once saw a 16 or 17 inch crenicichla, locking lips with some other fish, I can't remember what it was. Probably a large dempsey, or maybe even a Jag.. in a 4 or 5 foot tank, but, after the pike kicked the beans out of the other cichlid, it tried to turn and run, but it ran into the glass, stunned itself, and then got its eyes pecked out and rammed to death by the pike. All in a few minutes.
After I saw this incident, I decided anything but a Huge 200+ gallon aquarium, is inadequate for bruisers to live together in my home.
Lots of people do have successful large aquariums of bruisers, I just don't want to attempt a real group of bruisers, until I can provide at least 6 feet to run.