Ridgerunner, that's some good insight. I've thought of a few interesting differences that may explain the aggression. Here's more info. I didn't want to go overboard with details in my initial post.
I raised two batches of chicks. The first 22 chicks were a mix of Ameraucana, blue and black marans, blue and black orpingtons, and heritage turkeys. My friend got her 24 chicks from the same hatch, a mix of Ameracauna, crested polish, swedish flowers, orpingtons, and a few other heritage chickens.
At 1 month, I moved my chicks outdoors. They free-ranged with my 7 mature hens (who were very tolerant, though perhaps unenthused about them), and roosted in a separate pen. At this 1-month mark I got a batch of 14 turkens (Naked Necks). Another month later, the 2 month old chicks were integrated and roosting with the hens and the 1 month old turkens roosted in the chick pen. When the turkens hit 2 months they were integrated with the rest. So my chicks grew up with large, mature hens who kept them in place, and also grew up outdoors and with another age groups of chicks. I haven't had a single incident of blood or damage from bickering or fighting. None of the roos breed the pullets, only the actively laying older hens who now accept it.
The 'alpha roo' of my flock is a black maran. He and one of the blue marans were spit-fires from day 1. The black maran was displaying breeding behavior and bullying from 2 weeks old. At 2-3 months he went through a phase of attacking the dog. However, he has since stopped displaying aggression towards the chickens, the dog, or me, and just crows, breeds, and keeps a good look out. The blue maran roo is the second most well developed cockerel, however he doesn't crow or breed. It's actually the black maran and two turken cockerels who do the breeding.
My friend raised her 24 indoors for 2 months, with supervised outdoor time. All of her cockerels were displaying fighting/dominance behavior at about a month, whereas I rarely ever saw the "jump and lunge" cockerel antics. She moved them outside at 2 months, and her hens tried to kill them, so they were penned up and separated from the hens. At 4 months they were split up into two groups (on different ends of the property) and finally integrated with hens. This is when aggression started. And I mean BLOODY attacks between roos and roos against hens and pullets. So the roos were separated from the hens, and attacks escalated between males. So culling happened.
Maybe the combination of not having mature hens to establish order, and the separation of the chicks created an imbalance.
Also, I haven't medicated my chicks in any way, shape, or form. They were raised almost completely outdoors with lots of fresh fruit and veggies. My friend kept to strict 'by the book' diet, I believe she used medicated feed. She had an outbreak of coccidiosis (despite very clean living, I will say) and the birds had a round of antibiotics.
She's owned chickens for a very long time, whereas this is my 4th year with birds. I know she knows a lot more than I in many areas, but she's baffled by the aggression this year. She hasn't seen such aggression in past years.