For one thing, the page is at Miriam not at Miriam (biblical figure) or some other disambiguated title, so unless there is some other that could contend for being the primary topic  the question of which Miriam is the primary topic has already been decided. In the case of Alf no case has been made for Alf and Alfhild as the primary topic. Simply because something is the oldest known example does not mean it is the most well-known, which is the main criteria for primary topic status. Alf is an ambiguous term and I don't see that any of the Alf listed on what is currently at Alf (disambiguation) qualify and significantly more notable than any of the others.  ≠ wiser