Actions don’t have a return value. It’s not at all clear what an action would return to Shortcuts, and the APIs to return values are a bit limited at the moment and not flexible about returning different types of values.
You happen to have an action that modifies text, but that’s not really typical of what actions do in Drafts.
There are many ways to get a result back to Shortcuts. The Drafts action could put text in the cllpboard, as @sylumer mentioned, but also write to files, or store results in a draft which could be fetched. Lots of options.