There's no change in caffeine content with different roasts, this is a popular myth. Also, properly roasted dark roasts are much better (where better means richer and more complex) than light roasts, as the maillard reaction has been allowed to do it's magic more fully than under-roasted (or light roast) coffee. Most coffee specialty roasters sell far more City or Italian roast than light roasts.

This whole "dark roast is bad" thing is really Starbucks fault, since they burn their dark roast for consistency reasons.

https://www.kickinghorsecoffee.com/en/blog/caffeine-myths-da...

https://www.partnerscoffee.com/blogs/news/roasting-and-caffe...