Hey, this is me!
Something I found interesting about the response to this comic is that I made it without having any one story in mind, because it's a gripe I have with so many stories. But it received a lot of comments like, "This is obviously about X" with "X" being a wide variety of different stories, many of which I haven't even watched/read. Which I think really shows how prevalent this theme is in fiction.
As mentioned by others, this is something that exists (to varying degrees) in Star Wars, Harry Potter, Naruto, Bleach, and so on. Even Dragon Ball eventually got in on it. Goku just started off as some random monkey boy that Gohan found in the woods. In Z we find out he's actually descended from a race of super space warriors (the most standard among them, Raditz, still being more powerful than any Earthling). Eventually, we find out about Goku's biological father, Bardock, who is also the one saiyan who actually rebelled against Frieza, and with further specials dedicated to him, may be the original Super Saiyan (though non-canon) and just seems like (along with his wife) the one Saiyan who was actually a decent person.
May I ask what part you specifically "don't agree" with? I absolutely understand why these stories are written and why people enjoy them, I just don't think they're ultimately good messages to deliver. I generally have an aversion to stories where the protagonist relies on an external source of validation to affirm their value ("You actually do have value as a person because your ancestors were very valuable people!"). I also feel like this kind of worldbuilding creates a rigid class hierarchy that's completely dependent on familial connections. I have no problems with that sort of society existing within a story, but I don't like when the narrative supports its existence unquestionably.
I agree that the initial premise of Theophilia Wallace would still support a "born-with-it" message of empowerment, but that's only if the story stays on one level of subversion. Not that I'm disagreeing with anything more that you're saying, but my frustration with these kinds of stories is that when I start to notice "blood-based class structure" themes, I'm eagerly waiting for the story to subvert that theme in any way. In this sense, the little girl reading is my author avatar, "Oh! I know the story on the surface seems to support this unjust societal structure, but I'm sure that somehow Theophilia's character is going to be used to expose its flaws and upend their beliefs!"
Except more often than not, the story doesn't go in that direction. Society is correct that capability is an inborn trait, they were just wrong in determining what Theophilia's birthright was. Similarly, a lot of the stories that disappoint me in this regard have clues a lot earlier that this will probably be the theme, but I give too much benefit of the doubt and assume those are just misdirection.
Yeah, these are some ways this sort of narrative could subvert the "inherited powers" trope while delivering a message of empowerment that I find more to my tastes. Something like this is what I imagine the little girl reading is trying to predict in her mind. But she's going to be disappointed later on because she unfortunately expected the story to be more clever than it really was.