In the beginning, the hunters know how to firebend pretty well, whereas in TLA Zuko learned that firebending is about understanding the colorful, life-giving properties it has rather than fueling it with hatred. The hunters just use it to get food, and you don't see them develop through becoming a firebender, even though they use firebending for 24 hours> at a time.
i'm confused, are you talking aobut the dudes from the origin story? because a bunch of doofus hunters punching their fists to make a flame fart does not mean they bend well and does equate to the same amount of mastery wan gets when he trains with the dragons. especially when the lion turtle only gives them the bending when they leave the city to go into the spirit wilds.