Actual terrible worldbuilding:
Dividing populations or civilisations into really uniform, arbitrary segments. YA Novels love this shit.
Obviously mileage may vary. But for me, having actual chaotic, organic-feeling civilizations and communities gives a lot more opportunity for interesting individuals, conflicts, ideologies, etc.
They tend to be very Rock-Paper-Scissors, too (or Rock-Paper-Scissors-Lizard-Spock) with any superiority of one 'guild' or 'faction' technically vulnerable to some plucky-underdog quality that's only suppressed due to historic imbalance (possibly a then-coup, or a rise willingly agreed to due to circumstances, by the current (de facto?) governing lot). It can be seen prominently in wide examples of fiction such as the Minbari in Babylon 5, the world of Divergence, the Avatar[1] societies.
Usually the initially (once the story is set up) is solved by a 'saviour' from either the most suppressed element (by caste-like inevitability or 'sorting hat'-like assessment) or even totally outside the apparently stable system (but maybe assumed 'lesser element'-aligned upon arrival, if only because no-one else deigns to claim them) who agitates somehow. Maybe by being omni-capable (the Avatar-type, always intended to balance things) or unusually able to form cross-faction alliances (also Avatar, perhaps, but there are even better examples) to assemble the Captain Planet meta-power to re-balance the unbalanced.
Not that an RPS system is
bad world-building (however many elements, 3, 4, 5, 9[9] you use), but it can be a lazy shortcut. I've previously concocted a Bastard Mod mafia game (not on this forum), based on tripartate circular-supremacy, that failed more due to my inability to justify the seemingly conflicting results and interests. I've also got a long-standing universe-simulating project (or possible game, but never to be released publicly, I suspect, given it's been 30 years since I first came up with the concept) that uses a handy colourspace shortcut to three different tendencies (let's call them War, Growth and Subtlety). In my case, at least, it's a contrived system for the sake of a system, and could be considered tuned
just to set up the problem that then needs solving.
Not that it need be done badly, either, but it does do a lot of the work in a story that (for young minds, especially) need incredibly well-differentiated factionating from the off. The Hogwarts Houses' split (another even-numbered system, perhaps more black-vs-white than others but even then not absolutely so) creates the factionalisation missing (or at least easily subverted) in the more dynamic and variously stratified Sunnydale High environment.
Creators may have many different reasons for setting up the system to play in (design to justify the plot, extract the plot
from the worldgen conclusion of the design, or many other interpretations) but it can be/seem much too curated and contrived at times.
(Surprised to see this in General, as I flicked through. Though quickly realised it wasn't an Upper Forums subject at all, and maybe not (after all) entirely a Creative Projects discussion. Depending on where the conversation leans.)
[1] a) not the sci-fi one, SFAIK; b) unusually based on
four factions, at least on the surface/until later.
[9] Not
quite as described, but the Weiss/Hickman creation of the Darksword world had nine 'magical' affiliations, but it was more 3D with seven 'standard' magical specialities plus "Life" (magical conduit class, seemingly powerless but necessary for greater magic than could be unfolded by a single specialist, who had become the supreme priest-class government because of supply and demand) and "Death" (actually "Technology", but long banned and all-but-destroyed, because... likewise... it could theoretically enable a different kind of greater works outwith the control of the Life lot;
and faction-independently, because anybody can use something as simple as a lever rather than get an Air-specialist to arrange a levitation, or use medicinal concoctions rather than Water-aligned healing-touch, and none of this needs Life to be involved). Still, you can see the definite workings of the intended balance/imbalance of setting to it.