Thank YouI have a large NHR cockerel and just recently added a bantam girl to the flock. I was worried at first too but he is not rough at all and the few times I have seen him mount her there is no fuss and she just gets up and walks away with no issue. I agree with the others that weight isn't necessarily an issue as much as the mating behavior of the male.
Our big guy is a gentle rooster he doesn’t bully anyone , not even the month old chicks. He is just a sweetheart, but the hens’ safety is priority.