I feel like people forget that lightning bendi being gatekept is a retcon, and a badly explained one that. At no point in the original show is it even vaguely hinted at that this skill is rare because of political meddling. Iroh highlights it takes coldness and skill to achieve and that's it.
The retcon itself isn't even in LOK, or even the comics, you have to read the artbook of the first season to know it, and even then, I don't think it does a good job explaining anyway. It says it was taught only to royalty *and* high-ranking military officers, and yet, only 3 people who just so happen to be the most skilled firebenders in both shows are capable of performing it.
A lot of people apply backwards logic to Ozai, Iroh, and Azula to say the only reason they're the only ones is because they're royalty (even tho the artbook also says military officers were also trained in it) when originally, the focus was put entirely on skill and lack of emotion.