Note that different students find different courses intellectually more or less difficult. For example, one student may find linear algebra harder than calculus, while another student may find linear algebra easier than calculus (assuming regular sophomore level linear algebra, not honors or upper level proof-heavy linear algebra). Math courses do not generally have high baseline workloads, but a student who finds a particular one intellectually difficult may find that s/he has to put in a lot more work on it than other math courses.