Sephardim were more influential before expulsion from Spain and Ashkenazim became – after.
There is general history trend here, as Northern Europe became stronger comparing with Mediterranean. There is a possible connection here with increased production of beans in N. Europe that was cross-grown with wheat. Population is generally limited by the amount of available protein, that is mostly coming from meat that requires a lot of grass, etc. Beans added to that, ad also lead to kitniyos (according to a T’Ch who researched this history).
Similarly, Ashkenazi lomdus reflects European science v Arab stagnation from renaissance and up. Bit I do have a lot of sympathy towards Sephardi derech that often addresses issues directly. As we discussed recently, a Sepahrdi graduate of Lakewood criticizes ashkenazim for lack of real lomdus – when you have a method that can reach any conclusion you want, it is not a method (this corresponds to Occam razor; Karl Popper definition of what theory is and to machine learning theories of degrees of freedom and VC dimension).