Spoilers ahoy, but realistically we are past spoilers on Harry Potter.
Luna and maybe Trewlany are the only two Ravenclaw that break the mold here/\ Peter Pettrigrew is the only Gryfindor that breaks the mold. Sure Slughorn and Snape were good Slytherin but they had to go through a redemption arc of sorts to get there.
Okay so any character that we learn about in depth, there is at least a 50% chance that their sorting was way off.
Most of the good guy characters as adults were put in Gryfindor.
Albus Dumbledore was a Gryfindor. He's not a coward, but his defining trait is not his bravery. As a young adult, he was most noteworthy for his great intelligence. As an older adult, he was famous for his magical discoveries. This is very Ravenclaw. He was hesitant to confront Grindewald because of preexisting loyalty. His lack of boldness is not very Grynfindor but his loyalty could be Hufflepuff. When Dumbledore was leading the resistance against Voldomort the core of his strategy relied on obscure magical lore unknown to most people. That's a very Ravenclaw strategy. As a young man or an old man Dumbledore is wise and clever more than he is strong and brave.
Hagrid is not a coward either, but his defining trait besides his big size is his big heart. He is fiercely loyal to Dumbledore, McGonagall, Harry, Norbert the Dragon, his giant half-brother Grawp, Aarag the Spider, Fang the Dog and Buckbeak the Hippogriff. Being loyal is a very Hufflepuff trait, but Rowling avoids putting characters she respects in Hufflepuff.
McGonagall was Gryfindor. We don't get as much character development as I would like. Her main character trait is that she is kindly but stern and very by the book. That's not something that neatly falls into any of the four houses, but if anything she is clever and wise which seems to be Ravenclaw. She certainly kicked the ass of the Ravenclaw door riddle and possessed a lot of obscure magic.
Lupin was Grynfindor. He needed his friends to get him out of his shell which isn't super brave. Back when he thought Sirius Black was a killer Lupin was too timid tell Dumbledore that Black knew secret passages into Hogwartz. That's downright cowardly. Lupin's defining trait is probably his methodicalness and intelligence but not his bravery. He should have been Ravenclaw.
Sirius Black is very brave and he flouts convention bravely. He is a rare adult that actually was sorted correctly.
Slytherin are supposed to be ambitious. It bothers me that nearly all the characters just have an ambition to be Death Eaters.
I should point out that Peter Pettigrew should have been Slytherin. Not because he ended up with the Death eaters. If you have ambition, but you also recognize your limitations, you best options is to lick the boots of someone strong and powerful. Pettrigrew didn't actually care whether the boots he licked were of a good guy or a bad guy.
Hermione is brave, but she is not defined by her bravery. She is defined by her brainy-ness. If anything she is less defined by bravery than a lot of non-Grynfindor characters like Luna, Cedric, and Cho among others. Luna is brave to stand up to convention but she does fit into Ravenclaw because she is always seeking to learn.
Percy Weasley is not very brave, but he is very ambitious. He's not a coward pe se, but he certainly isn't defined by his bravery. He came from nothing and was set to advance himself via hard work and sacrifice, essentially setting aside friends and family to satisfy his ambitions. I don't know whether it was book one or two when he read a book about Hogwartz prefects that came into positions of power. He should have been Slytherin.
The rest of the Weasleys fit in Gryndor pretty well, at least the kids. I think Arthur Weasley and Molly Weasley lean slightly toward Hufflepuff, but I guess anyone family oriented would lean that way as adults. Then again, the unique form of Molly Weasley boggart signifies bravery. In my opinion people who fear for their loved ones far more than they fear for themselves are very brave indeed.
Though I suppose I think the vast majority of adults would have a boggart that either shows dead loved ones or some abstract insecurity like Lupin's full moon obsession.
Harry and Neville are certainly very Gryfindor. From what little we known, Seamus and Dean fit okay. Apart from Ginny, Hermione, and Luna we have very little characterization for any girls, so I cannot really judge if they were Sorted right.
Ambition can be used as a force for good. Slughorn mostly shows how ambition can be used for good. A teacher probably shouldn't show that much favoritism, but it's not lie Slughorn is corrupt. He genuinely wants to help the Slug Club and he puts qualified people into useful position and provides sage advice.
Draco Malfoy and his whole family didn't really have much ambition. They basically wanted to coast on their family name. I guess Draco wasn't very smart or brave or loyal or wise so he ended up in Slytherin by default.
Crabbe and Goyle didn't have much ambition. Of course they didn't have much bravery or brains either. They did have blind loyalty, even if was misplaced. Evil Hufflepuff! That's be an interesting nuance, they are in Hufflepuff but are mostly loyal to the family's of Deatheaters so they hang out with Slytherin kids every chance they get. Sadly, Rowling doesn't deal in this sort of nuance often.
So many Slytherin turn evil that it makes me wonder why Hogwartz tolerated them. You don't have to
kill them, but as soon as the Sorting Hat shouts "Slytherin!" you should throw them out into the muggle world as opposed to teaching these psychopaths magic powers.
It bothered me a lot that when they were taking student volunteers to fight off the Death Eater hordes,
zero Slytherin volunteered. Standing up to great odds is very ambitious. Hypothetically let's say you have ambitious Slytherin student whose parents are
not affiliated with the Death Eaters. They probably had to walk on egg shells in the Slytherin dorm for years and was both scared and angry at the position they were put in. In such a case such an individual should have boldly proclaim "Mahrlect you! I'm fighting for Hogwartz you monsters!"
Just like in Disney Star Wars I wished the explored the many character facets of a rebellious stormtrooper I would have liked to see a Slytherin character or two with depth. Jumping to Star Trek Deep Space Nine I would have loved to see a Slytherin character in the mold of Elim Garak with a similar will they/won't they redemption arc though
maybe Slughorn would qualify.
Anyway there are way too many people that don't seem to resemble their House traits at all. A friend pointed out that if the Sorting Hat puts people in a house based on the traits they admire, and not necessarily the traits they have, then the sorting results make a little more sense.
Peter Pettrigrew and Percy Weasley vaguely admired courage at least even if they didn't have much courage. Early in Book One, Hermione does say "Gryfindor sounds like by far the best" but the people she admires are all brainy by the books people, so that's fuzzy.
Again, if you go by admiration than Slytherin would be people who admire badguys. Maybe one in four eleven years olds admire bad guys. I remember being eleven, a lot of the other kids were mean. In this case Hufflepuff really leans into "I'll take the rest and treat them all the same" because no eleven year old admires Hufflepuff traits. Most eleven year olds either want to be superheroes or supervillains. Maybe a tiny number admire geniuses but Hufflepuff would be the truly ambition-less children who admire nothing and no one.
I think random sorting would actually make more sense but then it's harder to characterize supporting characters if you cannot fit a house stereotypes.
I really like Rick Riordan's books. He wrote alot of stuff but is most famous for the
Percy Jackson series. First off, while most people say the Harry Potter books are richer and more indepth the Harry Potter movie, most people say the movies were still enjoyable (though splitting book 7 into two months was not a good idea in my opinion).
I will warn people that the two Percy Jackson movies were really bad. The first ten minutes of the first Percy Jackson movie was awesome when Zeus and Poseidon came down to Earth to parley, but after that they ran out of budget for both special effects and A-list actions.
The gist of Rick Riordan's fantasy world is that remember how in Greek mythology the Greek gods were banging mortals and creating demigod children a lot? Well even though people don't worship the Greek gods anymore they are still around and they still are siring demigods.
In a way, you can draw an obvious parallel between the Percy Jackson's cabins and Harry Potter's Houses. In Rick Riordian's world, kids are sorted by the godly parent.
The Athena kids are in all Cabin 6, the Apollo kids all were in Cabin 7. Etc. The Ares kids were arrogant bullies and the Aphrodite kids were vain and flighty. Given the rivalry between Percy Jackson and Clarisse LaRue of the Ares Cabin 5 you could kind of argue that the Ares campers were roughly equivalent to Slytherin.
The difference is while the Ares kids were arrogant bullies they had redeeming characteristics. Like true children of Ares they were barely tolerable during peace time but during times of conflict they were brave and loyal defending all the campers, even their rivals.
The Ares campers were useful enough when the chips were down that the other campers tolerated their rabble rousing. The Hermes campers were useful enough when the chips were down that the other other campers tolerating their constant theft and pranks. In other words, all the camps had strengths and weaknesses and all had something to contribute.
Contrast with the Harry Potter universe. Despite the two or three decent Slytherin people the House produced, House Sytherin is collectively dead weight at best, a liability at worst.
I better get back to managing the current short story contest, then when the voting is started I can come back here and complain about more things I don't like about the Harry Potter universe.
I should note, that while I enjoy tearing the Harry Potter universe into tiny pieces, I do it out of love. There is an expression about romance that you like someone for their good traits, you love someone for their flaws.
I'm not sure if that applies to people or not, but for me it applies it art. If I
didn't like the Harry Potter franchise I would not point out all it's flaws. I don't like Dr. Who, so I don't bother analyzing it (I don't
hate Dr. Who, if you are fan I do not wish to offend you). I strongly dislike like the Kelvin Universe Star Trek (all the stuff released this century), so I don't bother analyzing it, but I
do like the 1990s era Star Trek so I will analyze the flaws of that. If you are a fan of Dr. Who I will shrug my shoulders and say "To each his/her own." If you are a fan of the Star Trek Discovery (aka STD) then you are wrong, very wrong. But that's a topic for another thread.
But again, I eviscerate Harry Potter out of love.
If you guys want to start a Percy Jackson/Rick Riordan thread, I can eviscerate it out of love too. Rick Riordan writes new books a lot faster than JK Rowling ever did. My main complaint about him is that his new books are very similar to his old books. He copies and pastes his basic formula a lot. I wish he took more risks. Riordan let his teenaged son write a short story in a Percy Jackson anthology. His son is going through an edgy phase, so
he wrote something risky.
(she has other qualities 
) 
