I currently use it for:
- My personal blog with 250+ posts and tons of pages[0]
- A podcast platform[1] which is open source[2]
- The landing pages for all of my web development courses (not going to bother linking them since I don't want to seem like I'm fishing HN for sales)
I also recently wrote about my whole site's tech stack here[3]. That post might not fully apply to you since you want to host it on S3. I personally self host everything on DigitalOcean but using S3 wouldn't be a problem.
You mentioned "static assets" and this is where Jekyll shines IMO. The jekyll-assets plugin (optional) will md5 tag your assets for cache busting and bundle your scss / JS too. It's really handy and avoids having to set up more complicated tools. It pretty much works out of the box with close to zero configuration.
The plugin system is nice too. You can do some really useful things like automatically add certain rel attributes to external links with a few dozen lines of Ruby. It's very handy for a blog.
[0]: https://nickjanetakis.com/
[1]: https://runninginproduction.com/
[2]: https://github.com/nickjj/runninginproduction.com
[3]: https://runninginproduction.com/interviews/1-100k-page-views...