That's indeed a good idea.
I was like that too "hmm , so now imma choose one Eidolons of atleast 3-4 Eidolons...great ^_^" but then , Sigrun's key.... I can say also that I don't like her look that much as other Eidolons, and also I don't really need her abilities but rather I'd have an assassin's one or healing one .
It would be nice if they let us choose. Atleast ,if they won't , then they must change the dialogue .