I recently took a class in elliptic functions and found the theory of elliptic functions very clean. You get very powerful results and the proofs are usually short and intuitive. Then we learned about modular forms where the proofs became less clean but were still fine and still yielded nice results. But when we finally covered theta functions/jacobi forms, the proofs boiled down to nothing more than "plug it in and simplify the gigantic, ugly, random terms". This went on for multiple lectures and happened in every lecture that touched on theta functions. Is this really all there is to this theory? Just simplifying ugly algebraic expressions to obtain more ugly algebraic expressions?
We were told that theta functions are a hybrid between elliptic functions and modular forms. I thus expexted their theory to be a mix of both theories. But instead, it resembles neither.