Here’s the open secret about Starbucks. I worked with a former manager who was not a crazed leftard so he had to leave. They over roast the beans so they can use less and still get a bitter taste. In reality, dark roast coffee generally has less caffeine than lighter roasts since the longer you roast beans the more volatiles are driven off. Equal weight of the same variety and a light roast will have more caffeine than a dark roast.
Less caffeine, more ashtray! Yum!