You're missing what I'm saying.
Picking the least aggressive of a bunch of roosters is different than just getting rid of the most aggressive - the difference is in how you treat the middle. If you're just getting rid of the most aggressive roosters, you're keeping the ones that are right below that threshold in the gene pool. If you cull down to the least aggressive rooster, you're getting rid of those middle birds. It's a much more significant selective pressure.
Agreed!!! after having a mean rooster many years ago I decided never again, so when we went down the road of wanting to expand our flock we found a good rooster, problem is, he is a bit timid.. We had a problem with a hawk that would make a daily run for chicks.. One day I was out in the coop and watched this rooster (huge blue orpington) run and cower in a corner when the hawk appeared.. finding the middle ground is more important for us that having a docile rooster...