>>148969735thats only the genetic component, bending is a spiritual and supernatural phenomena. You also have to consider Aangs relationships, if he was some petty arab dictator that wanted a harem then sure, but having a a legion of breeders would ruin his relationship with Katara and create a lot of useless bastards with a axe to grind with both the fire nation and their "father".
Not only that but those type of arrangements even create contempt between the "chosen" siblings, it would be like giving birth to a dozen Zaheer's
Giving birth to air benders is one thing, raising them to be good stewards of the culture is another. Aang needed Gyatso to teach him and raise him properly, even as monk he had a father/grandfather figure that taught him the airbender path.
Human culture and society doesn't work when you treat people like livestock. Tenzin did it right, he picked a non bender wife and had as many kids as possible raising them all carefully to follow the path; if all of his kids do the same they will restore their people and culture.