Looks like I missed all the fun last night.
No strong opinion as to the testosterone theory, but what I have heard and read is that the old cockers bred away from human aggression in their birds, and that was their livelihood, how they paid the bills.
Myself personally, I think part of why I gravitated toward Brahmas was the fact they were so much easier than Dad's Cornish. Not always hell-bent on going extinct. Wanting to fight each other at any opportunity, not being able to get off their backs if they did get flipped, poor layers, late fertility (lot of clear early spring eggs), even poorer hatches (fertile eggs that failed to hatch), and so forth. That being said, I still have a pen of the project blue laced red large fowl Cornish going.
Something I found kind of interesting at the 2014 Ohio National show which hosted the national meets of both the Cornish and Brahma clubs (along with many, many others). I am a member of the American Brahma Club, but also sat in on the Cornish club meeting as well. Some members of the Cornish club got rather cantankerous about points of parliamentary procedure during the business part of the meeting which seemed to linger through out the duration of the meeting. Where as the Brahma club meeting, any similar conflict was put to a vote, and on to the next topic of discussion. So I guess some folks do gravitate toward a breed that may more closely resemble their own true personality.