Is it a coincidence that both book series had a protagonist with a “saving people problem”, by which I mean that once someone even suggests that someone they love is in danger, they will risk everything to save them.
Both times, it ends up being deconstructed as a flaw. It puts Percy into danger and makes him hesitant to run away, often threatening his life in an already dangerous world. It actually ends up being used against Harry when he’s shown a fake vision of someone he’s close to in danger, and hastily rushes to save someone who was never in danger in the first place, which Ironically leads to that person dying.
Did we just identify with protagonists like that and had to have characters like Superman deconstructed for us?
A strength in a character also being a flaw is a literary trope from way back.
One of the classic examples is in Sophocles. Oedipus is an aggressive and curious, highly intelligent man. His aggression and restless intelligence serve him well as he is not intimidated by the sphinx, easily guesses irs riddle and claims his prize (the hand of Jocasta). However it is also his aggression that caused him to not submit to the authority of the man who turns out to have been his father, and prompted Oedipus to kill him and his servants, and his relentless curiosity that uncovers the incest he himself is guilty of.
Shakespeare also dealt with the fatal flaw trope, Macbeth is a man of action who excels at making quick decisions. This quality is balanced by his loyalty and humanity. The tragedy is both his and his wife’s : she urges him to act in his own interest, and to hell with loyalty and humanity. As a result he dispenses with these qualities and his best quality turns into his worst as he turns into a ruthless tyrant, who massacres whole families on a whim and doesn’t even care when his wife dies. Her love and ambition for him, her own fatal flaw, turns him into a monster and she dies mourning the absence in her life of qualities she had previously scorned.
I think it was Coleridge who pointed out that if you had put Othello and Hamlet in each others’ play you would not have had a play. Each would have solved the other’s dilemma in five minutes. Othello would have walked straight up to Claudius and stabbed him, and Hamlet would have had one conversation with Iago and walked away saying “that guy is full of shit, and he fucking hates me”
These are all examples of tragedies, but heroic fiction (which is the genre that both HP and PJ belong to) is often basically tragedy with a happy ending. The fatal flaw/character strength which is also a weakness is also a trope in fiction largely because it’s a thing in real life : any strength carried to extremes becomes a weakness, and a strength is only a strength until it isn’t. People often excel at one area of life and so do that thing in preference to other activities, even when it isn’t appropriate. “If your hand is aa hammer, everything looks like a nail”
Superman, by contrast, has no real weakness, apart from the fact that he cares about other people. That’s partly why he is intrinsically a far more boring character than the troubled Batman, and the reason why an external weakness of kryptonite was retconned some time after his creation as a plot device. Stories need conflict and resolution, and a character that incorporates those qualities is just inherently better written and more interesting than one who has it as a clumsy add-on. FYI it was created not in the comics but in the subsequent radio series.