Despite Kirihara's awesome placement (and Dabuz' impressive, yet expected, essentially solo-Rosa result), solo-Rosa has recently been trending downward. Whether that's due to player inactivity or some combination of other factors is uncertain, but the trend is still there. I'm not going to go through and graph every top Rosa player's placements over time, but if you keep up with her meta you just kinda feel it. ¯\_(ツ)_/¯ I'll try to elaborate a bit.
Dabuz uses an alarmingly (alarming for me as a dedicated Rosa main) large amount of Olimar in top8/16s nowadays, and seems serious about Bayonetta. Players just seem to be optimizing anti-luma strategies and finding subtle ways past Rosa's toolbox. That's expected to a degree, but her advancements don't seem to be keeping up. The early upair kills happen less. Town and City isn't an auto-pick in a lot of matchups anymore (notably vs fox). Rosas are trending toward picking longer stages over ones enabling good juggle opportunities- neutral is getting harder and retreating space is appreciated more and more, while the juggle kills don't happen as frequently. In general, we're increasingly focused on picking stages that minimize disadvantage and give us more chances to win neutral play, rather than on exploiting our strong advantaged state. You may attribute that to taking the usual, necessary steps to optimize risk:reward, but I see it as a way to 'stop the bleeding' in a sense. In many cases, other characters seem to use the platforms better.
Matchups. More of her high/top tier matchups are slowly dialing back into even or disadvantage territory from what were once viewed as slight to healthy advantages, than vice versa. Some example include Cloud (it's even or disadvantage), Mario (slowly from a solid +1 for Rosa to a slight advantage for Rosa, or even), Diddy (opinions vary, but most think it's even at this point), Lucario (I personally strongly disagree with others, and think Rosa wins, but my opinion isn't shared by many), Fox (slowly making his way towards even where I personally think it'll settle in the end), Bayonetta (shifting more and more towards her favor). I'm more basing these off of opinions I've heard from top players of these characters, and a bit of my own competitive experience & analysis which I value greatly.
On the other hand, Falln's been less active at some points, but seems to be competing more, again. Rayquaza seems to be more active than he was roughly 6 months ago, thankfully as well. Kirihara seems to be on top of things as per usual, following that long hiatus earlier this year(?). I'm being vague on purpose- idk what their personal lives are like.
But I increasingly see a striking resemblance between Rosa's meta progression and Snake's back in the brawl days. Those large, confusing- a bit obnoxious- hitboxes eventually adapted to with better spacing and precise hurtbox placement. Also, taking bigger and bigger advantage of certain aspects of his disadvantaged state. But I also see parallels between her and Brawl Olimar in terms of Luma/Pikmin mastery, and Olimar skyrocketed up the brawl tier lists so.. ¯\_(ツ)_/¯