Hello, I am actually an economics major (concentration in finance) at Duke currently so I might be able to provide some type of insight into the major and department!
One note before I begin: If you love both majors, do both! SOO many students double major (including myself in Econ/CS) and wouldn’t have it any other way. Additionally, if you want to go into any type of finance or banking, I do not see a way you would not major in economics (with finance concentration). With just political science, you most likely would be buying your self a one-way ticket to either law school or consulting. Not that those are bad things (I am pre-law), it is just not what you want if [banking] is your goal.
First, I would like to point out a key difference in the department that I was not fully aware of going into Duke: there is a significant difference in classes and culture between the traditional economics major and economics with a finance concentration. The finance concentration is still the same BS in Economics; however, it requires you to take finance-specific electives that will land you with roughly 2 more classes to satisfy the major completely and a significantly different set of qualifications in economics upon graduation.
Want to go into any type of finance (ESPECIALLY investment banking)? You will be doing the concentration and it will be incredibly helpful to you, no question about it.
Let’s talk about difficulty…
Duke Economics is hard. In terms of classes, you will find yourself being challenged by most, if not all, of the “core” economics sequence unless you are a genius (I know some, you might be). When it comes to beyond the core (electives), they are all different but none of them will be “easy”. A lot of people will complain about the “math” making economics hard and they are right. I do not even know how to begin with our math department. It is HARD. Every class, from, calculus I on up, is incredibly challenging if you do not truly LOVE math with all of your heart (the math majors). I know you said you have satisfied your math requirements; however, if they are not AP Calc (AB and BC, 5s), you will have a TIME getting them transferred and if you do convince them, don’t be surprised if they force proficiency examinations in calc I/II, multivariable calc, and light linear algebra. They will gladly take the AP Calc AB/BC credit; however, I do not know anyone who got to skip out of multivariable calculus at Duke. Additionally, I doubt you would want to skip out on MATH202 (multivariable calculus for economics), which is a hybrid class between multi and linear algebra. You want to be used to rigorous math because you will encounter it in economics classes (remember, a lot of economics professors majored in math in undergrad and you will see it).
Most likely, your GPA will get dinged a couple of times (mine has more than I would’ve imagined) and that is FINE. Remember, Duke is one of the top schools for economics/finance in the country and world. Your instructors will AMAZE you every day and you will learn so much that goes beyond a good GPA. The connections the university has will make sure you are not out of a job, come senior spring. Many seniors I know that have GPAs toward the bottom quarter of finance people still are heading to places that our peer institutions have to work hard to get there people into.
Should you expect lower grades, even if you work hard? Better to be pleasantly surprised then feel like crap when that final grade is uploaded. It depends on you but I would not expect perfect grades.
POLITICAL SCIENCE! It is a fantastic department and if you love the subject, you will love the classes. I am not an expert about the department but I have many friends who are and they enjoy it. If you have any questions about it, I can speak to what I know or ask one of my friends. Remember that economics is a STEM major. Many people forget that. Which makes it VERY different from the other social sciences and humanities. It depends on what your knack is! Ok, I am officially rambling.
To conclude, if you have any more questions, I am happy to answer them, here or in DM! Additionally, if insight into these departments is crucial to your college selection or you are incredibly implored to learn more, I am happy to speak through a more conversational medium.