Actually, “Lightning Generation” is a subset of Firebending. Re-directing lightning is the method Iroh developed by studying Waterbenders.
Right now, the Avatar Wika lists Mako as one of the five known lightning generators. I don’t believe that’s accurate, since we’ve only seen Mako re-direct lightning.
Point being, until Mako says something about generation vs. redirection, we haven’t seen enough of Lightning Bending in the new series to distinguish if re-direction has been popularized alone because it involves inter-disiplinary training (which would make sense in a city where firebenders and waterbenders live together) or if general wide knowledge of bending has allowed more people to learn special subsets.
