Debian lets you switch and AFAIK it mostly works fine. They provide both sysvinit and runit as alternatives. Packages are only required to provide systemd units now, however a lot of core packages still provide sysvinit scripts, and Debian provides a package orphan-sysvinit-scripts that contains all the legacy sysvinit scripts that package maintianers have chosen to remove from their packages.

That’s just in the official repository, of course. Third-party repos can do whatever they want.