The biggest difference besides the programming model is scale. Luigi and Airflow target data pipelines that don't require much scale. Cadence is built to support business level transactions. It can handle tens of thousands of events per second and hundreds of millions of open workflows. Obviously it is also a good fit for low scale use cases. Cadence is also so generic that it can be used to implement practically any workflow definition language. For example it is possible to create an extension to run Airflow pipelines on Cadence.

I'm from the Cadence team.