I agree that this is an important distinction, and that things that might naively seem like mechanisms are often actually closer to descriptive models.

I'm not convinced that RL necessarily falls into the class of things that should be viewed mainly as descriptive models, however. For one, what's possibly the most general-purpose AI developed so far seems to have been developed by explicitly having RL as an actual mechanism. That seems to me like a moderate data point towards RL being an actual useful mechanism and not just a description.

Though I do admit that this isn't necessarily that strong of a data point - after all, SHRDLU was once the most advanced system of its time too, yet basically all of its mechanisms turned out to be useless.