The caffeine difference due to roast levels is mostly disproven afaik. Roasting destroys caffeine but light roasts are more heavy so if you brew by weight, that equals out. Also, caffeine content tends to vary a lot by variety and type. Robusta beans have a lot more caffeine than arabica. So if you drink a traditional italian dark roast espresso, that still can have more espresso than a light roast specialty espresso. James hoffman made a video once about that where he ordered different espressos at different coffee shops, both specialty and traditional chains, and tested the caffeine levels and they were all over the place