My gelding is the same way with other horses--currently, we have 17 acres to turn out 11 horses on, plus 3 pasture boarders at the barn. With all of that space, what does he do? Beats the crap out of everyone except this little mare who can fit under him...she's the boss of him. He's had no bad experiences with horses, he just thinks he's the big man on the property and wants the mares for himself....when they are in heat he goes as far as to 'protect' them from the other geldings. I unfortunately have no idea when he was gelded, I purchased him almost 3 years ago and he has always been liked that. So he's turned out by himself, or if we have a cocky baby coming in for training, they get put out with him for a bit to learn some manners. He doesn't mind being out there by himself as long as there's grass. -shrug-
Instead of introducing them all at once, I would pick one, the bottom of the two geldings, and introduce them separately and let them figure out who's who then throw the other gelding, then the mare into the mix. It was probably a sensory overload moment for him... and he is obviously a 'fight' sort of horse.