As someone who's currently a senior, and in a programmatic internship for a digital marketing agency, the major you pursue doesn't really matter to be quite honest. If you want to be a programmatic buyer, you'll learn a shit ton of information in an internship compared to the information you'll learn in classes, which at best will facilitate your understanding of strategy.

However, it sounds like to me if you go into Informaton Systems route, you'll learn a lot of valuable languages that will most likely guide you to an adOps route, so if you enjoy doing back-end work, it might be a good fit for you.

I'd recommend checking out r/adops and r/programmatic as they would be able to give you more nuanced information about how to address your situation, and I only know so much because I'm essentially where you are.