I mean...
"Secret cabal of Airbenders that survived the genocide" has been a fandom plot since the beginning. The idea that a few Air Nomads survived, hid, and had kids in secret (thus thinning the bloodline and suppressing the airbending genes) really isn't t hat far-fetched.
It's also consistent, because yes. Bending is genetic. There's a reason you don't have Earthbenders popping up in the Water Tribe, and while there is a spiritual aspect and Bending probably can't be mapped to a Punnett square very easily, if you don't come from a lineage of Earthbenders you won't be able to bend earth. Toph may have learned from the badgermoles but that doesn't mean her ancestors weren't already Earthbenders. Shes' from the Earth Kingdom, it's pretty inevitable.
And look, prodigies? Are also genetic. Being a prodigy doesn't mean 'really good at your job', it means 'having a preternatural talent', which is informed by genetics. That doesn't mean hard work and dedication can't help somebody who isn't naturally talented become very, very good at something, but that's not the same as being a prodigy. That's just being very, very good at something.
It also doesn't mean you can learn something if you have NO propensity toward it. A non-bender cannot learn to be a bender through sheer hard work and dedication, just like not everybody in the real world can be an athlete.
I do appreciate her superficial message of 'you have to work hard to get what you want', but given her own propensities -- thinking everybody she likes (including herself) should be given everything they want without doing any work, writing her characters by just making them super strong out the gate and making, at best, vague gestures that they tried really hard to get there while she herself doesn't put in the work to show it -- leads me to believe it's just based on being a dick to the fandom. "These buffoons are so obsessed with bloodlines because, obviously, they just want to work for what they earn!"
No, Lily, they talk about blood lines and natural talent because the show itself has supported these. Bending is not spontaneous. Bending talent IS genetic. Azula was as strong as she was BECAUSE the Fire Lord's line practiced selective breeding-- Ozai chose Ursa as his wife BECAUSE she was the daughter of Avatar Roku and therefore they would breed powerful children. It's literally in the lore.
And, like I said, it's not like all of Lily's characters aren't born into privilege or else handed what they want. G was the result of an IV breeder who also gave her powers that Gardevoir don't normally have. Aliana might have moderate midichlorian numbers but her mother was the most powerful Force user of her time and taught her everything she knows and also left her a heap of holochrons she could instantly learn from. Iris got a Master's in psychology entirely off-screen. Anevay became the most powerful Hoard warrior entirely off screen. Niva is able to Earthbend so hard she snaps her sister's bones on the regular when she gets scared. She may superficially say that her characters aren't special and they had to work hard but she doesn't actually show it and hands them whatever they want with minimal difficulty besides.
And while I'm thinking about Niva:
Niva can Firebend because she's filled with anger
...why?
We don't see this. Anywhere. Niva is constantly scared and Lavi constantly has to step in to help her. All we know is that Niva is a 'smol bean' constantly clinging to Lavi's arm yet we're supposed to believe she's also boiling over with righteous indignation? Obviously being scared and reliant and being angry aren't mutually exclusive but nothing about what she's actually written for Niva supports her being prone to anger and therefore 'passion'.
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