Alpha angelfish are almost always male. Within a few weeks, they are twice the size of their brothers and sisters. They are the ones that learn the quickest and are the pushiest when it comes to food and survival.
Omega angelfish can be female or very passive males. They are the smallest angelfish and usually stay away from the others in their group. You'll often seeing them going their own way - when their brothers and sisters are crowded at the surface of the water to eat, they are at the gravel level, or hiding amid the landscape.
If I'd allowed the parents to remain with their young, they would have killed and eaten the omega angelfish in order to give the largest and more robust babies a better chance at survival, which also means less competition for food.
Because I separated the parents very soon after their babies hatched, it gave all the fish - even the omegas - a better chance at survival, because there are no predators and there is plenty of food for all. In the video below, you'll see the variety in size between the alphas and omegas.