Trait is ignored. It's rarely if ever portrayed in entertainment, sometimes not mentioned in nonfiction either. Members may or may not realize they belong to this group, depending on how obvious it is, or that anything meaningful could be derived from acting cohesively as a group. People just don't think it's important. Or, they think it's inferior.
If they haven't already, people make fun of the trait. There are snotty jokes and stereotypes. It begins to leach in from the fringes, often appearing first in the least sophisticated and polite sectors of entertainment.
The trait becomes a little more visible in the form of stock characters. These are stereotypical, usually negative, and usually brief appearances. They are not main characters. They are not dimensional, do not grow or change. On the rare occasions something else happens, it is criticized as implausible, pandering, bad literature, or some other excuse.
Actual people with the trait begin to reach out to each other and talk about doing something regarding all the oppressive bullshit going on. They complain about the crummy representation. They discuss what kind of improvements they'd like to see in their own lives. They are dissatisfied that there are few or no decent reflections of them in entertainment. They want to do something about this.
So they start rocking the boat. This annoys and scares the people in power. That leads to more negative portrayals.
But some creative people think, hey, maybe these folks have a point. They start exploring more diverse portrayals of the trait. Which they then have a hard time selling.
Some folks with the trait also start expressing their own experiences. They may band together to share cultural material that is not acceptable to the mainstream. At this stage, stories with trait-having characters tend to be About Trait. It's so conspicuous that it steals the show from almost anything else, unless you're, say, blowing up the universe. Anything more than a bit player drags the trait into The Theme. It also tends to be very gritty stuff, because they've been through hell.
As the social movement gains momentum, so too does the shift in entertainment. More portrayals, now containing a mix of negative, some neutral, and early glimmers of positive characters emerge.
Long about this time, enough data accrues to start identifying patterns, such as plot devices and character types. The first stop-trope complaints arise as people with the trait point out that certain motifs are damaging, repetitively dull, and/or otherwise annoying. People want to take pride in their trait and are sick of being told it's icky.
The mainstream catches on to the idea of the trait in a more serious manner. Some real advances are made in social justice. More nuanced portrayals begin to emerge as characters are no longer static and one-dimensional. Enough of a pattern has been established for it to be interesting when something breaks in a different direction.
By this point there are likely to be clusters of creativity producing a regular supply of material from inside the trait. At first the mainstream mocks these as lesser quality than conventional material. This may in fact be true. Early writers in a field are often people-with-trait-who-write rather than writers-who-happen-to-have-trait, etc. It can take quite a while to develop a really skilled canon, especially if the trait puts people at a real disadvantage for education and prosperity. Around here is when the first awards are likely to appear.
The stuff gets better over time. Eventually the mainstream decides that this is cool and politically correct and profitable, so starts releasing bunches about it, some of which is worthwhile and much of which is insulting crud. But now there's enough built up that a determined person can actually find a handful or two of great content. This is really helpful for people-with-trait who want to understand it, and how it may affect them, and what some of their options are for dealing with the experiences of trait-having. Because that's what cultural material does, it helps us examine ourselves and think about situations before they actually happen to us.
Presently, the shiny wears off. People have seen enough of trait-having characters that it's no longer such a big deal. They've mostly gotten it through their heads that the trait exists, isn't evil or irrelevant, and doesn't always have to be a big deal. Characters and concepts continue to become more refined, complex, and realistic. And this is where background parity arrives: a character can have the trait, and it can just be there, like hair color or whatnot. The story doesn't have to be about that.
This is frequently the point where some other trait or issue starts gaining a lot of attention, and bigots and activists go haring off after the new target.
The cool thing is, this progression is endemic to cultural material in general, and probably to the human condition. So if you know about it, then you can spot new versions as they emerge. This means you don't have to sit around with your thumb up your butt waiting for everyone else to plod through A, B, C, etc. You can just go directly to the good stuff.
This means, if you're a trait-haver, start telling your story as precisely as you can. Your experiences are relevant and perhaps historically important. If you're not, try to find people who are and do good enough research that you can step over the bar (which is pretty much lying on the ground for a while) and create or request things that are plausible, nuanced, and entertaining. There will be some screaming about how you can't or shouldn't do this. Unless it is along the lines of "You fucked up this detail!" from a trait-haver, or "I'm going to shoot you!" from a bigot with a gun, ignore it. People are going to scream about this trait and trait-havers for a while. Like a decade or few. They will calm down eventually.
Meanwhile you will be creating or inspiring some great stuff, which by dint of early appearance and hopefully quality, will become part of canon and might just help save somebody's life by advancing the timeframe of when "Trait-having doesn't have to ruin your life, look, it's possible to have-trait-and-be-hero!" becomes available to folks in need of that as counterbalance to the "trait=awful or irrelevant" baloney in the mainstream. Plus you get to poke a bigot in the eye, and that never gets old.