WHY does warrior cats have a background-character problem anyway?
& a defence of one-note characterization
in my post about nominative determinism, I made the case that the Erins should use the naming conventions of the series to establish very simple characterizations for their background characters.
a potential rebuttal to that would be "this would be make the background characters very one-note". That's true; it's also desirable.
When I say background characters, I mean BACKGROUND characters. Not even your Lionhearts and Runningwinds that I mentioned in the post; I'm talking about Leafshade, Eaglewing, Stemtail, and so forth. Characters who are unlikely to have more than two or three mentions PER ARC.
The problem isn't that they have simple characterizations--it's that they have NO characterizations. Right now, they are zero-note characters.
A series with an ever-changing team of writers and editors needs simple, one-word, static characterizations. Each Clan needs a stock pool of characters: someone to be annoying at Gatherings; someone to hate kittypets; someone to defend kittypets; someone anxious about fighting; someone gung-ho about fighting; someone helping around the medicine den; someone who takes care of the elders; someone who takes care of the kits; someone who imitates the Clan leadership; someone who builds dens; someone who gossips.
These characterizations can be easily communicated. Many of them apply to existing tertiary or background characters throughout the series: Daisy, Berrynose, Thornclaw, Brightheart, Dustpelt, Spiderleg. Those characters enjoy much more attention and recognition from the fans, because even if characterization is one-note, that one note provides a foundation to build on--either for the fans to build on, or for the Erins to build on and sell more novellas, graphic novels, and SEs.
So why doesn't this happen more?
One answer is that the series is not very well-written. That's true, but I do think the fandom tends to put too much weight on this as the answer to everything and also identifies the wrong things as symptoms of bad writing.
Like I said above, this is actually something that the series has done in the past! We have had eras of ThunderClan where the majority of the characters have at least one adjective that can be reliably applied to them. So a better question is:
Why did this stop happening?
Characters' relevance is constantly changing, and the writers are not always the ones who get to decide who will be important later on. This motivates them to keep every background character as a completely blank slate.
From the glimpses we've seen into the Erins' and Working Partners' writing process, it seems that the actual authors of the books don't get all that much of a say in how things shake out. Edicts get handed down from on high about who gets named what (Sparkpelt), who gets to EXIST (Cypresspaw and Wavepaw), and who the main characters of each arc will be.
There was no implication in TBC, for example, that Sunbeam was about to take the reins as the next arc's protagonist. She is a zero-note background character. If the Erins had risked making her the "annoying at Gatherings" character, they would have had to reckon with that in her POV or create a continuity error in her characterization.
Most of the interesting aspects in the series have occurred through these kinds of "continuity errors." Because you know what a continuity error can become when you write in that character's POV? CHARACTER DEVELOPMENT.
Here's a sampling of characters who were clearly intended for one thing and then got thrust on a new course when the series either continued beyond its intended ending, the opportunity to sell a novella/SE from that character's POV arose, or they suddenly became relevant through a relationship to a protagonist:
Breezepelt. He is very obviously set up to be the Clan cat who is a true believer in the Dark Forest, and he is chased off at the end of OOTS, presumably never to return. BUT, OOTS didn't end up being the final arc. And hey, we didn't actually KILL him, so let's use that drama as the premise for a Crowfeather Super Edition.
Tigerheart and Dovewing's relationship. Also obviously intended to end in OOTS (because everything was intended to end with OOTS), then resurrected for AVOS and Tigerheart's Super Edition.
Blackstar. Reread Into the Wild and tell me what kind of character Blackfoot is supposed to be. He's literally abducting children as fodder for the war machine. He's presented as the thuggish second in command to Brokenstar, the epitome of evil, destined for the same kind of death as Bone of BloodClan. But when the narrative demanded a new leader for ShadowClan, and the opportunity arose to give him a tragic past and a redemption (and to sell a novella), the authors took a left turn.
Berryheart. She was a background character in post-OOTS ShadowClan, and her notable actions include getting saved by Guardian cats and naming one of her kits after them. When ASC gets going, suddenly there's drama in the fact that she is one of the most outspokenly nationalist (clanist?) cats around. This conflicts with her prior characterization in an interesting way.
There is AMPLE PRECEDENT for a character starting out one way and then being jerked in another direction because the series calls for it. The authors (and WP presumably) shouldn't be afraid to repurpose characters and create these "continuity errors," because those "mistakes" provide fertile ground for interesting characterization.
Avoiding giving background characters any characterization out of fear of what Working Partners might later demand of those characters creates a different, much worse problem
the blank slate to main character pipeline
The pre-main-character-stasis of characters like Sunbeam and Bristlefrost (apart from their identical romantic subplots) is comparable to where Rusty is when Into the Wild starts. But beyond nostalgia, there's a reason TPB is beloved and these later arcs feel hollow.
Triple-POV arcs means each character has a third of the opportunity of Fireheart to establish their plotlines and characterizations. Firestar got 6 books of development; each protagonist in the last three arcs gets the equivalent of 2 books.
That's why the Erins should make these new protagonists come in with lives ongoing, in medias res. How do you make that happen? You stop leaving every background character as a blank slate. Give them one-note personalities, and then when Working Partners tells you "Sunbeam is up next!" you have ALREADY taken the first step in establishing who she is.
A "blank slate" isn't as neutral as it sounds; if we have already heard this character's name, met their family, read their description in the allegiances, all without getting any sense of them as a character? We don't think nothing about the character, we think of the character as nothing.
Rusty worked as a blank slate because he was the audience surrogate. We didn't know anything about the world, so we had to learn through Firepaw. That hasn't been true for OVER TWENTY YEARS. We come in already knowing about the world; we need to know something about the character too.