Ah, you have pointed out one of the problems I get with the over friendly roosters.Showbirds are a whole different ballgame. For one thing, they've been raised and trained that way from early on, and often part of the criteria in choosing a showbird is a calm disposition. But even so, it is no guarantee that a show rooster won't turn on and attack an owner when it is in its own environment and it feels its dominance is being threatened. It happens all the time. It has happened to me. And judging by the number of posts seen on here of tamed roosters attacking their owners, I'd say it is a very real problem.
I guess it all boils down to what you want, in the end. I definitely do not want most of my cockerels acting like pets and going limp if I touch them. They need to be tough and ready to deal with constant competition and the threat of predators. So not taming them makes sense for me as a way to avoid aggression. But if the original poster wants her cockerel to become a tame pet, then yes, with a lot of time and training it is possible. But it is still no more of a guarantee than any other way of dealing with cockerels that this bird won't turn aggressive. There really are no guarantees, only things to avoid to make aggression less likely to appear.
Much like you write, I really need fairly aggressive roosters if they are going to be flock protectors given the chickens here free range. I struggled with this a number of years ago with the first orphan rooster I had.
When this rooster grew up he was great to handle, would come when I called him, was very polite to the hens, but as a protector he was a pile of ****.
It wasn't until he had to fight the bully rooster here that he grew a set. so to speak.
He's not great at protecting now, but he's a lot better than he was.