Fitbit has announced that all current fitness tracker and smartwatches now support stress management. Previously, Fitbit reserved the functionality for the Luxe and the Sense.
https://www.notebookcheck.net/Fitbit-brings-its-stress-management-feature-set-to-all-its-fitness-trackers-and-smartwatches.533614.0.html
You're right; Fitbit is being way too stingy about non-premium features and the premium subscription is a terrible value. Having a premium subscription is the worst thing Fitbit has ever done.