I consider all those things and experience tells me they aren't as prevalent as you think. More often than not, it is coaches applying this reasoning without even having given it a chance or without having ever seen any such repercussions.
Boys these days are less "girls have coodies" than they used to be. So many boys are soft from playing computer games that there isn't as much of a gender disparity in sports on a day to day basis. My DD and another girl would dominate boys in playground soccer with no downsides. Shoot, I grew up with such a girl. Never saw a boy refuse a rematch just because he lost.
Go out to a track and field training. Boys and girls race side by side. Slow boys get beat by fast girls, yet they come back to practice the next day.
Why spend so much time justifying these antiquated thoughts? Is the problem really how the boys will feel, or is it just another case of "everyone gets a participation trophy" rearing its ugly head?