Hogwarts houses make a certain amount of sense. You sort students into groups based on a degree of compatibility. They were invented by medieval wizards, so if the groups they settled on turn out not to be very conducive to getting pre-teens and teens to get on with one another, that’s fine. Sure, it’s a bit of a design failure in universe, but as a setting element it makes it very easy to establish different cliques in a hurry and it’s appealing to a young audience who are still trying to figure out exactly who they are as individuals because it gives a finite list of options to sort through.
Its major failing is that there was a strong theme of all the houses of Hogwarts needing to unite in the face of Voldemort, but it turns out there was an asterisk on that theme, and the footnote said “except Slytherin, fuck those guys, they’re evil.” This particular theme is supposed to be about bringing together lots of different people in opposition of hatred and terrorism and all the other things Voldemort brings in his wake, but since all the protagonists are Gryffindors, their allies in Hufflepuff and Ravenclaw are quirky sidekicks rather than major characters, and all Slytherins are evil (except for one, who is a defector who turned his back on evil after graduating, not someone who was simultaneously Slytherin and proud and also opposed to Voldemort), what you get is a story about Gryffindor vs. Slytherin in which two other houses are shadow divisions for Gryffindor.
Divergent takes this basic formula and, rather than fixing up the broken bits, instead completely cocks up the whole thing.
The basic problem with most Hogwarts house clones in YA is that they adhere way too strongly to what should have been a Hogwarts-specific conceit: The good guys are the clique defined by bravery. Being defined by bravery can lead to heroism and it makes sense that the Hogwarts house that accepts brave people happens to end up being the good guys, but it would make just as much sense for Hufflepuff, defined by loyalty and friendship, to be the ones who stand in most rigid opposition to Voldemort’s campaign of genocide, or even Ravenclaw, because if any of them know their history (and really wizards don’t seem to learn anything but magic, but if they do) they’ll know that xenophobic regimes never end well even for the alleged “master race.” Things don’t get better for one group at the expense of others, they get worse for everyone, but especially for minority groups, so the chosen group only does better by comparison to their neighbors, not by comparison to what they could’ve had if they never bothered imprisoning the muggleborns to begin with.
So right away you know something’s gone wrong if the protagonist ends up in a faction defined by bravery. There is no reason why such a faction would necessarily be leading Team Good. It’s a possibility, but in any work not written by JK Rowling, it’s a bad sign of copying Harry Potter wholesale. Divergent begins to avert this by having the faction defined by bravery, the Dauntless, be a bunch of insane psychopaths who care about strength and fearlessness without really caring about helping people at all, but other than this one vague gesture towards “bravery does not always equal heroism” it’s running dead-on into all the problems of a Hogwarts clone.
Blatantly evil faction depicted as being fundamentally villainous, thus (accidentally or not) vilifying the ethically neutral quality they’re founded on? Check.
Conflict is primarily driven by a clearly evil faction (Erudite) fighting against a clearly good faction (Abnegation)? Check.
Other factions are ultimately shadow divisions of the main two defined by character quirks with no goals or beliefs in any amount of opposition to whichever of the main factions they swear allegiance to? Check.
In fairness to Divergent, the book does occasionally flirt with rising above these problems, but the other end of fairness is that Divergent tends to cause new problems in the process. The book is named after people who are capable of being at home in multiple factions. This diverges (no pun intended) from the Harry Potter formula, but only in a stupid way. Harry Potter has the Sorting Hat indecisive over where to put many different students. When the hat can shout out a student’s place immediately upon being put on their head, that’s weird. It’s more typical for the hat to debate for a while, and while it’s not entirely clear, from the way Harry’s sorting went, it’s probably having a telepathic conversation with the student to try and sort out with them which of several possible options would work best. Harry could thrive in both Gryffindor and Slytherin. Hermoine probably could’ve been a Ravenclaw, Neville probably could’ve gone Hufflepuff, Cedric Diggory probably could’ve gone Gryffindor, etc. etc.
Divergent shakes this up by acting like having any potential at all for multiple different categorizations happens to a minority of people. By doing this, Divergent puts the burden on itself to come up with a means of categorizing people by which it really is most typical for people to be cleanly sorted into the different groups, with little or no potential to embrace the ideals or talents of the others. That is an extremely tall order, and Divergent does not make that mark.
Similarly, Divergent early on makes some gestures towards painting a faction driven by bravery as being potentially villainous, but then repeatedly shoots itself in the foot. It turns out that Gryffindor/Dauntless’ relatively recent change in culture away from “help the helpless” towards “only the strong shall survive” is the result of Slytherin/Erudite infiltration, and even then, the changing culture does nothing and they end up seizing control of Dauntless via mind control technomagic instead. Just like with Harry Potter, all factions but Slytherin/Erudite are shadow divisions of the good guys. The good guys are Abnegation instead of Dauntless, and by the time the story starts the Dauntless are heavily infiltrated by Erudite, but even so, the Dauntless are not persuaded to join the coup. The Erudite don’t promise them more wealth when they’re in charge, which is usually what would-be coupers offer to the military to get them to support the coup. The book even discusses the basic idea, with a lot of Dauntless people expressing a degree of support for Erudite having more say in government, that maybe things would be more prosperous if the smart people were in charge instead of the selfless idiots who think all luxury is decadence (and either don’t know or don’t care that command economies are grossly inefficient, but the book never makes that point, specifically). They shoot themselves in the foot at the climax, though. What should have been Dauntless just signing up for the Erudite cause because they want stuff is instead Erudite using sinister mind control to force them into joining the coup. So turns out Dauntless was a shadow division of Abnegation all along. The sequels are going to reveal that Amity is also a shadow division for Abnegation remnants, and also that Candor briefly pretends to be neutral before ultimately also being a shadow division of Abnegation. We haven’t talked about Amity and Candor because they are like Hufflepuff and Ravenclaw in that they don’t matter except as shadow divisions for the main good guy faction.
In fact, there’s not any apparent difference at all between Erudite and Candor except in that the former is evil. In theory they’re supposed to value intelligence and honesty, respectively, but in practice Candor is depicted as valuing knowledge and open debate while Erudite are…academics and journalists, so the same thing, basically. Sure, it’s perfectly reasonable for Erudite to be corrupt and to be misusing their apparent control over news media to advance a self-serving agenda, but assuming that Erudite, the faction founded on intelligence, is smart enough not to let their marks know they are being lied to, what exactly is the difference between Erudite and Candor in principle? Remember, they’re different pillars of the same dystopian command economy, so they can’t be competing truth-seekers each claiming to be more reliable than the other. That would make sense, it would be totally reasonable to have a setting where the subtle difference between seeing truth as a resource to be controlled (Erudite) and seeing truth as a virtue to be upheld (Candor) is explored, but Erudite and Candor are part of the same overarching bureaucracy. One wasn’t started up in competition with the other. They both believe in the importance of knowing the truth, they both engage in investigation and debate to determine the truth, the only difference is that Candor abhors deception whereas Erudite is ambivalent about it. They aren’t even particularly deceptive as a faction, because most of the shitty things they report Abnegation getting up to are actually completely true. Abnegation really does turn a blind eye to child abuse, and there is no reason at all that Erudite rather than Candor would be the one to release the report on that except that Candor doesn’t seem to have the infrastructure. Not only does Divergent have the thing where one of the factions is clearly and inherently evil, they’re the same faction as one of the others, except evil. It’s like if Hogwarts had a fifth house whose founding philosophy was about aspiring to greatness and success, and just never commented on how that is basically identical to Slytherin except without being racist against muggles.