The point is whenever there is a chumra people say “Well chashuv rav So and So did it that way, dont you want to be like chashuv Rav So and So”
Well when a Rav doesnt do a Chumra people make all sorts of excuses why he did it . I think we can agree that Rav Shlomo Zalman did not take Culas and knew the Halacha well.
Its not in the regular Haggaddah, Its in the Haggadah of Rav Shlomo Zalman Auberbach. It came out after his death