Crowding can diffuse aggression of American as much as with African, but the scale is different. Have you seen large Midas coexist peacefully in 300+ gal tank in youtube or in public aquarium. Midas max out to 15 inch, Mbuna 6 inch, so you need proportionally much bigger tank to achieve crowding harmony.
Cichlid living in group in the wild doesn't make them more peaceful or more amenable to crowding management. Mbuna and Tropheus live in large congregation to graze algae on rock in the wild, yet they are the most aggressive species in respective lake. Predatory haps that spread out in the wild are the more peaceful species in captivity.
Few people keep solitary Africans because they are small fish. But I have kept one 6 inch Chipokee in a 10 gal after he killed every one in the community tank. He is a glass banger and attack even his own reflection.
I've never had luck crowding large aggressive cichlids. It seems to work for some but not for others. I've never kept Africans because I've been too busy keeping CAs for the last 29 years. What would I know?