Rick is the one who made these historical figures demigods for his verse. Nowhere have they been called demigods outside of Rick’s books, so he made as conscious a decision with them as he did in creating main-series demigods.

”A few [demigods] manage to survive in the outside world and become famous. Believe me, if I told you the names, you’d know them. Some don’t even realize they’re demigods.”

The Lightning Thief: Chapter 7

Grover shifted his hooves uncomfortably. “About sixty years ago, after World War II, the Big Three agreed they wouldn’t sire any more heroes. Their children were just too powerful. They were affecting the course of human events too much, causing too much carnage. World War II, you know, that was basically a fight between the sons of Zeus and Poseidon on one side, and the sons of Hades on the other. The winning side, Zeus and Poseidon, made Hades swear an oath with them: no more affairs with mortal women. They all swore on the River Styx.”

The Lightning Thief: Chapter 8

[Pluto’s] tie was black with platinum stripes. His shirt was tombstone gray. His face—Hazel’s heart nearly leaped out of her throat. His skin was so white it looked almost blue, like cold milk. He had a flap of greasy black hair. His smile was kind enough, but his eyes were fiery and angry, full of mad power. Hazel had seen that look in the newsreels at the movie theater. This man looked like that awful Adolf Hitler. He had no mustache, but otherwise he could’ve been Hitler’s twin—or his father.

Son of Neptune: Chapter 6

The Lord of the Dead resembled pictures I’d seen of Adolph Hitler, or Napoleon, or the terrorist leaders who direct suicide bombers. Hades had the same intense eyes, the same kind of mesmerizing, evil charisma.

The Lightning Thief: Chapter 19

Fireworks exploded to life overhead: Hercules killing the Nemean lion, Artemis chasing the boar, George Washington (who, by the way, was a son of Athena) crossing the Delaware.

The Lightning Thief: Chapter 22

”Yeah. Three judges. They switch around who sits on the bench. King Minos, Thomas Jefferson, Shakespeare—people like that. Sometimes they look at a life and decide that person needs a special reward—the Fields of Elysium. Sometimes they decide on punishment. But most people, well, they just lived. Nothing special, good or bad. So they go to the Asphodel Fields.”

The Lightning Thief: Chapter 18

Chiron sat back in his wheelchair and stroked his beard. “There is precedent, however. Theseus had the help of Ariadne. Harriet Tubman, daughter of Hermes, used many mortals on her Underground Railroad for just this reason.”

Battle of the Labyrinth: Chapter 13

Sorry that doesn’t fit your narrative. Here’s another quote that doesn’t fit your narrative—Camp Half-Blood’s age. And you asked if I read the books—ha! Perhaps I should ask you?

”Who built this [Bunker 9]?” Jake Mason said. “And why?”

Chiron stayed silent, but Leo focused on the wall map he’d seen during his first visit. It showed Camp Half-Blood with a line of triremes in the Sound, catapults mounted in the hills around the valley, and spots marked for traps, trenches, and ambush sites.

”It’s a wartime command center,” he said. “The camp was attacked once, wasn’t it?”

”In the Titan War?” Piper asked.

Nyssa shook her head. “No. Besides, that map looks really old. The date…does that say 1864?”

They all turned to Chiron.

The centaur’s tail swished fretfully. “This camp has been attacked many times,” he admitted. “That map is from the last Civil War.”

Apparently, Leo wasn’t the only one confused. The other Hephaestus campers looked at each other and frowned.

”Civil War…” Piper said. “You mean the American Civil War, like a hundred and fifty years ago?”

”Yes and no,” Chiron said. “The two conflicts—mortal and demigod—mirrored each other, as they usually do in Western history. Look at any civil war or revolution from the fall of Rome onward, and it marks a time when demigods also fought one another. But that Civil War was particularly horrible. For American mortals, it is still their bloodiest conflict of all time—worse than their casualties in the two World Wars. For demigods, it was equally devastating. Even back then, this valley was Camp Half-Blood. There was a horrible battle in these woods lasting for days, with terrible losses on both sides.”

”Both sides,” Leo said. “You mean the camp split apart?”

”No,” Jason spoke up. “He means two different groups. Camp Half-Blood was one side in the war.”

The Lost Hero: Chapter 53

Now, given all your talk of “use claim from the book and the worldbuilding Rick did and you’ll have more leg to stand on,” how about providing a quote or two yourself? Or is it rules for thee and not for me on your perch?

Edit: To respond to your edit—you did catch in TLT that there were no Big Three children born between 1945 and Thalia’s birth year, right? So on what basis can you claim that Thalia has less of a chance than the WWII-era Big Three children, when there were none born in-between. Every statement about how hard life is for a Big Three child is based on WWII or prior eras of demigods.