That's a distinct possibility. If hatcheries can prevent cockerels from forming, they don't have to do away with so many. (I won't go into what some hatcheries do....)
Again, I think this is a confusion; Most boys (which are already set out to be boys) will do very well in high temperatures; Most girls (which are already etc. etc.) will do very well with lower temperatures, increasing each sexes' chance of survival.
X2
Basically, the temperature never decides the sex; rather, it favours one sex or the other. Higher temp: boys will all survive, most girls won't. Lower temp: Girls will all survive, most boys won't. Something like that.