Deployments are a significant amount of magic, moreso than with other languages. You're deploying a whole beam ecosystem not just a single app. If you want to do anything remotely dynamic (e.g. using environment variables as knobs a la 12-factor) you'll have to rely on distillery and voodoo.
Meanwhile distillery has been broken on FreeBSD for months with no fix in sight and no actual community understanding of how things fit together. Dockyard also has a good blog post explaining how complex Elixir deployments get:
https://dockyard.com/blog/2018/02/28/elixir-deployment-tools...
No bueno. Generating a WAR or JAR to deploy is typically trivial in comparison. Capistrano? Easy peasy AND reliable. Distillery? I'm just glad I don't have any production Elixir apps.