I did not downvote you. I think it's wonderful that people love the UI of SourceHut. You've put a lot of effort in and made a product that many people love, and that is fantastic and a hell of a lot more than I can say for myself. Seriously, congrats on all you've accomplished, and thank you for all you've done for the open source community, it's quite a lot and very deserving of appreciation
But my point is about mass-adoption. What I personally think of the UI isn't very important - as you say, "Design is in the eye of the beholder". But I would argue that if GitHub were to release a redesign identical to SourceHut in 2020, we'd see the largest exodus of GitHub users (for personal projects at least) ever - far, far, FAR more than any other time GitHub has changed their UI.
You can argue that GitHub and GitLab have UI that degrades a developer's experience. You can argue that their designs are FADs, and even that eventually they might change their design to be more similar to your's. And all of those arguments may be right. But right now, I'd argue that this design hurts mass adoption, and even though what design language is "in style" is completely a FAD, following the FAD does help adoption, and entire companies (e.g. fast-fashion like H&M) make tons of profit on FADs (even when they do horrible things - like how fast fashion is bad for the environment, some of GitHub's actions are bad for open source, the Apple example, etc).
I think your numbers are great evidence that you will get users with your current design, and I think that were you to release a GitHub clone (design-wise), you'd lose most of your users and would still struggle to gain non-GitHub users. I don't think there's a way to satisfy both camps of users, but perhaps a "colorful" and "minimal" theme may help? This is not as important as other things you are doing such as the things mentioned in https://news.ycombinator.com/item?id=25103662 but I do think it would help with mass-adoption (which may even be a non-goal, or may be far less important than other goals - that's totally fine too, I'm not trying to judge you or say you're completely wrong, just pointing out something which I feel is missed in these design discussions on HN).