Regarding Apache and nginx, you're referring to the sites/mods-enabled mechanism? Actually I really like that one compared to the "stock" way of one damn yuge httpd.conf - way more maintainable, no matter if in a Docker container creation script or in a bare-metal environment with Puppet provisioning.

Regarding exim... exim is one of a nightmare no matter how one looks at it. I hate it with a passion, no matter the distro.