I'd love if you jumped into our Discord/Slack and brought up some of the issues you were seeing so we can at least make the experience better for others using Dokku. Feel free to hit me up there (my nick is `savant`).
Let me preface and say that I'm an application dev with only a working knowledge of Docker. I'm not super skilled at infra and the application I struggled with has peculiar deployment parameters: It's a Python app that at build-time parses several gigs of static HTML crawls to populate a Postgres database that's static after being built. A Flask web app then serves against that database. The HTML parsing evolves fast and so the populated DB data should be bundled as part of the application image(s).
IIRC, I struggled with structuring Dockerfiles when the DB wasn't persistent but instead just another transient part of the app, but it seemed surmountable. The bigger issue seemed to be how to avoid pulling gigs of rarely changed data from S3 for each build when ideally it'd be cached, especially in a way that behaved sanely across DigitalOcean and my local environment. I presume the right Docker image layer caching would address the issue, but I pretty rapidly reached the end of my knowledge and patience.
Dokku's DX does seem great for people doing normal things. :)