Maybe some are imprinting due to be handled, hand fed and petted as chicks? This article has a paragraph about male birds.... http://www.usask.ca/wcvm/herdmed/applied-ethology/Bottle-raised%20males%20can%20be%20very%20dangerous.pdf
After reading about that topic so often here on BYC, I've noticed most of the posts involve young males that were handled or hand fed as chicks, folks describing them as affectionate, gentle, babies, etc. that turned to attacking their owners upon sexual maturity. I have to wonder if a lot of it was a result of that early imprinting and resulting confusion. Maybe some cockerels are more prone to imprinting than others which could explain the varied results you are showing. It would be worthy of an experiment on deliberately ignoring male chicks during the formative months, no handling or hand feeding, etc to see if that tends to continue or if it's truly a line or breed issue.
I've heard that theory often and have wondered about it myself, but I truly don't believe it's as simple as coddling the boys too much. I handle nearly all of my birds a lot, and I've got half a dozen roosters, full-grown roosters, that are as affectionate with me as any puppy and still do an amazing job of taking care of their girls and protecting them from danger, including from people they don't know. They don't attack other people, but they are cautious around them and tend to move the girls away from them until I make it clear that everything's okay. I think some animals are just wired differently.
I had one Barred Rock rooster, Shadow, that was the meanest of any I've raised. All of his male progeny have shown varying degrees of aggressiveness, from full-on attack mode to what would be more akin to flightiness. When I cross him with the BR hens I'd raised with him, his son wasn't AS aggressive, but was still pretty bad. When I cross his daughters to a completely different rooster that tended towards keeping his distance, the off-spring showed some hostile tendencies, but was easily trained to stop attacking and to instead simply keep his distance. For about 2 weeks that boy would lunge at my feet and ankles and peck, but after two days of working to correct his behavior he's been good as gold. I still have him, as I'm growing him out more before butchering. He's dominant in the bachelor pad and literally herds the rest of the boys away from the door so I can bring them food and water, and keeps his distance until I close the pen door again. So there's one experiment...
I have also reduced my handling of a few of my NN cockerels, more out of time constraints than anything else, but haven't observed monumental differences in behavior beyond an increase in nervousness and evasiveness. Whereas my other NN boys are respectful if not downright friendly, he keeps his distance and does all he can NOT to be handled. I've only ever had one mean NN rooster, and he was delicious. His son, while slightly more nervous, is very sweet and friendly, though he prefers to "talk" with us rather than be handled. He tolerate handling, but doesn't seem to find it very dignifying.
That's the extent of my own experience and observation to date. I too would love to see genuine research on the matter, but I suspect it would have to be breed specific.