Hogwarts Houses: Stereotypes

I've thought about this long and hard, and after being sorted a Slytherin in Pottermore and learning of the many admirable qualities of the House, and all four Houses in general, I've come to my conclusion. I absolutely love the Harry Potter series, but they were biased in favor of Gryffindor and Ravenclaw.

And I know, yes, it's told from the point of view of a Gryffindor, but even then, it was kind of strange to me that every house fit its stereotype so strongly, yet Gryffindor was the only house that was full of merit, with very few people defying the House stereotype. Even Neville grew into his Gryffindor-ism. With the other houses, there were exceptions to the stereotype. For Hufflepuff, we had Cedric Diggory. For Ravenclaw, we had Luna Lovegood. For Slytherin, we had Draco Malfoy, who we learn is more than he seems on the outside, and Severus Snape.

I think the caste order of the Houses of Hogwarts were clearly set in an order. This is not my opinion of them, but this is how they were (unfairly) portrayed in the books:
Gryffindor - bold and brave and adventurous; why wouldn't you want to be one of them? (exemplified by- well, come on. Harry, Hermione, Ron, Neville, Fred, George, Angelina, I could go on)(counter-example: Peter Pettigrew)
Ravenclaw - smart, creative, intellectual, the brainy house
Hufflepuff - a load of puffballs. Why would anyone want to be in Hufflepuff? (exemplified by Hannah Abbott)(counter-example: Cedric Diggory, maybe Susan Bones)
Slytherin - no-good scumbags who cheat and do bad things to get what they want. ALL the bad wizard CLEARLY come from here. (exemplified in Crabbe, Goyle, Pansy, Voldemort, the Quidditch team, even Draco in one of the matches)(counter-example: Draco, towards the end of the series, Severus Snape)

So these assumptions about the House aren't just things that are said about them from the point of view of Harry- no, there are examples to prove the point.

When Pottermore came out, they Sorted users of the site into Houses. This is where, I feel, they tried to mend the stereotypes a little. If you read each House's welcome letter (easily found on Google), suddenly each house is full of merit and you should be thankful you were placed in this house as opposed to others.

For Gryffindor, the welcome letter was the shortest, which makes sense, because we've learned everything we need to know about Gryffindor already. It's from Prefect Percy, telling us in one of the lines that, and I quote,
"This is, quite simply, the best house at Hogwarts."
But that's just Percy speaking.

For Ravenclaw, the welcome letter just emphasizes the positive qualities we already know Ravenclaw to have. Pretty easy.

For Hufflepuff, it's a change.
"Our emblem is the badger, an animal that is often underestimated, because it lives quietly until attacked, but which, when provoked, can fight off animals much larger than itself, including wolves."
Until now, we have seen Cedric Diggory fulfill exactly what the letter talks about. But that's one person out of many. Don't I recall Hannah Abbott fainting during the O.W.L.s?

For Slytherin, here we go. These scoundrel Slytherins that we have met so far... they're suddenly not the dumping ground of the bad guys? Crabbe and Goyle and Pansy... this is what they are?
"Because you know what Salazar Slytherin looked for in his chosen students? The seeds of greatness. You’ve been chosen by this house because you’ve got the potential to be great, in the true sense of the word. All right, you might see a couple of people hanging around the common room whom you might not think are destined for anything special. Well, keep that to yourself. If the Sorting Hat put them in here, there’s something great about them, and don’t you forget it."
So what's so special about Crabbe and Goyle and Pansy? Where are their "seeds of greatness"? I think, in reality, they were placed in Slytherin because they didn't fit anywhere else, and were destined to be bad people, so there you go. Another evil Slytherin. Yippee. Oh, and apparently Merlin is from Slytherin now.
"Here’s a little-known fact that the other three houses don’t bring up much: Merlin was a Slytherin. Yes, Merlin himself, the most famous wizard in history! He learned all he knew in this very house!"
Another example of trying to make it seem more meriting than the people placed in it in the books.

If all of the above is true, that Slytherins are really just ambitious folk who play to win, and Hufflepuff is full of hard-working, loyal people, (which I'm sure is absolutely true, just not the way it's portrayed in the books), then why weren't Albus Dumbledore, Ernie Macmillan and Percy Weasley Sorted into Slytherin for their ambition?

I could be wrong, of course. There's one answer I've come across that can explain the weird Sortings. That people are Sorted not for the values they exemplify, but the values they, well, value.

However, overall, I think that the advantages of each House did not have well-placed people exemplifying those positive qualities. We had a handful from Slytherin, Malfoy, Severus; everyone from Ravenclaw was pretty much smart; we had Cedric showing off true Puffism; and, well, the majority of Gryffindor showed off their positive attributes.

This was just my take on it. I of course respect the character choices and Sorting choices, which can be easily explained by the values explanation, and I admire Pottermore trying to fix the stereotypes a bit, but I felt each House fit their stereotypes in the books, rather than defying it, for the most part.