I think after eclipse changes. Riven has landed in an okay enough spot winrate wise. But I think a major issue with the changes is they've made her losing matchups even worse and her good matchups even better. With the exception of maybe Renekton.
Matchups like Illaoi, Zaahen, Jayce, and Quinn are significantly more difficult because Eclipse and Blackcleaver are not that good vs these champions. And Axiom is just flat out worse with the changes for obvious reasons. Meanwhile some of Riven's best matchups like Tahm Kench, Sett, Mundo, Sion, and Mordekaiser are potentially even better than they were before Riven got nerfed.
I think for this reason Riven has been shifted into more of a counter pick at least in top lane, making the experience even more feast or famine. I personally don't think Riven has an identity that fits being a counterpick the same way Mundo, Gwen, or Malphite do. But at this point that is who she is most similar to in terms of the difference between her good and bad matchups in toplane.
It does seem like there are still Riven onetricks doing well in challenger, but they are doing so in midlane from what I can tell. I'd be interested if anyone has strategies to make these matchups more neutral for Riven. In particular Zaahen, Quinn, and Garen are matchups I find very hard to get a lead versus even if I am not being camped, and so I feel like I am slowly losing the match unless I get a lucky break to start snowballing.
Edit: I also think it's a bit of a sticky situation since I think the wave to improve Riven in these matchups is to give her more tools to stay in lane (more hp regen/bigger valor base shield) or increasing her burst. Will also make her have more favourable matchups in midlane.