The Beis Yosef is citing Rabbeinu Yerucham. Everyone agrees that that has halachic weight with regards to whether one can eat kitnios.
I don’t agree to that.
I think it has as much halachic weight as citing the passuk about how pesach is 7 days as proof that you don’t need to keep 8 days in chutz l’aretz.
How can citing a source from 800 years ago have any bearing on a minhag that has developed since then?