Since when are we following the rule of "one female character treated badly = the show, even if unrelated can never have a female protagonist"
We know that the anime can make a female co-protagonist front and center. Dawn is proof of that concept. We also know that traditionally, one of the few ways to distinguish a new main character from the old one is a contrast. For example, Avatar Korra is a hot-blooded, ready for action girl to serve as a contrast to her predecessor Avatar Aang, a peace-loving boy. You also have Rey and Luke Skywalker from Star Wars, Sam Wilson and Steve Rogers in MCU Captain America, Red and Yellow in Pokémon Adventures, etc. There are some similarities at the core, but many differences in on the surface. So when you look at Ash, the quintessential shoenn boy archetype of the Pokémon for over 25 years, his successor has to be very a distinct character, not simply a clone of Ash. And Liko has the right amount of balance between familiarity and freshness. You can tell she has Ash's spirit (with a Pokémon League symbol hairclip) but is clearly a distinct protagonist by her own right.
The difference between DP Dawn and Journeys Dawn is pretty apparent though. I don't think that Dawn was necessarily poorly written in Journeys, but the fact that she was so stagnant compared to virtually every other returning character made her stand out like a bad thumb. I don't think it's a case of just Chloe treated poorly either. After how Journeys and to a lesser degree SM handled its female characters, it does seem a bit strange for them to go for a female lead in this series. Dawn shows that they can make well written female leads, but after Journeys didn't even bother to have a proper female lead, I'm not confident that they can pull off Riko as well as they did with Dawn at the moment.
That's still a pretty bad sign though. If they couldn't even be bothered to give her a Typhlosion, or really any sign that her off-screen travels have resulted in anything more than a few more ribbons, then that doesn't give me more confidence about how they can handle a new female lead. That's why I brought up the differences between Dawn in both series. DP actually cared enough to give her consistent focus and screentime while despite appearing so much in Journeys, Dawn doesn't really get much to actually do. Obviously, I wasn't expecting Dawn to get a major storyline in Journeys, but my point is that despite being well written in DP, they couldn't really do much for her in Journeys.
I was thinking more about the writing quality of the SM girls and Chloe rather than just their treatment. I don't think that they were poorly written per say. Chloe in particular is both a highlight of Journeys and one its flaws at the same time and Lillie had some great moments in SM, especially during its first year. However, I don't think that the writing for the female cast in either series was particularly good. The series is going to follow Riko and her Pokemon, which would require consistent screentime and development ideally, but that doesn't mean that it will be handled well. Coming right after Journeys especially makes me more cautious about how they'll handle Riko. She could have a well written and engaging storyline and that would be great, but I don't have a lot of confidence after how the past couple of series have handled their female leads.
I'm positive that comparisons are going to be made regardless. I don't know about how much resentment it brought, but so many people were instantly jumping on the "Riko is Ash's daughter" theory and going by the clip in her hair being the same shape as the logo on Ash's OS hat. Perhaps it wouldn't be as direct or overt if Roy was featured more instead, but people are going to compare any lead with Ash regardless of their gender. Not to mention the inevitable "Which is the better protagonist?" question popping up sometime down the road.
Well, she is an exception, and none of her successors were shown anywhere close. And even Hikari had to share her place as co-protagonist with Satoshi and stand slightly backward to not overshadow him. Riko is the main character, female, and stand up front of Roy, it's something they never done before.
If she gets one of the Paldea starters as her first Pokemon, which is extremely likely if not flat out confirmed, I think that means that she'll be around for just this generation. She would still be associated with the ninth generation and they'd want to have someone feature the tenth generation starters instead.
Ash got the Kanto Starters, but that didn't stop them from having him go for as long as he did.
