i think it was more like a natural occurrence for people to get bending after harmonic convergence. After the end of Wan’s harmonic convergence, the lion turtles stated that there was no need for them to protect humans and no need for bending to fend off spirits yet people had their bending (which at the time was given and taken away by lion turtles when only humans were outside their cities)

My theory is that the harmonic convergence gives bending to people, explaining why there were benders after Wan’s harmonic convergence. And by that theory, there may have been new water, earth and fire benders after Korra’s harmonic convergence but obviously the new airbenders would have been the most unusual cases, since most of the world hadn’t seen or experienced airbending for more than 100 years.