If you're mainly just looking for something with Docker preinstalled VMWare's PhotonOS[0] may be an option. It's a stripped down CentOS/RHEL based distro that's targeted at being a container host. I believe they've said they'll also package other container runtimes in the future as the market shifts.
A quick look shows the ISO as ~4GB, which is a bit concerning though - CoreOS is around 450MB, and RancherOS only 135MB (although it's a bit difficult to compare, since they both download stuff during boot).
That's not the install size. From the documentation there are multiple install options ranging in size so they just decided to package it all in one. "Minimal" install is like 400-500 MB iirc.
[0] https://vmware.github.io/photon/