I'm sure this is right for someone, everyone has different requirements, but I don't really want a lighter-weight Airflow. I want an Airflow that runs and scales in the cloud, has extensive observability (monitoring, tracing), has a full API, and maybe some clear way to test workflows.

I was looking into how Google's Cloud Composer is run, which is a managed Airflow service. They use gcsfuse to mount a directory for logs, because Airflow insists on writing logs to local disk with no cleanup system, even if you configure logs to be sent to S3/GCS. To health check the scheduler they query Stackdriver Logging to see if has logged anything in the last five minutes, because the scheduler has no /healthz or other way to check health. There is no built it way to monitor workflows, so you can't easily do something like graph failures by workflow, email on failure is about all you get. A GUI-first app that requires local storage is not what I expect these days.