Interesting, I find it surprising there isn't a widely used service with this functionality.
You can do this with most static site hosts. I guess the only real concern is trying to get dynamic subdomains.
I even wrote a small server to accept tarballs and dump them onto the filesystem so that they could be served by nginx. https://gitlab.com/kevincox/tardeploy (sorry, no docs)
S3 doesn't offer the redirect functionally and you would have to have your aws keys public in the repo.
So not really substitutes.
Dynamic subdomains aren't a problem for this with the smart redirecting logic.