b. Being in a spin off title does not mean you aren't a supporting cast member. You might be a character in your own right but you are still part of a supporting cast. We just had a Batman story about whether the Batfamily helped or hindered him and Batamn's conclusion was that they supported him.
c. By your definition of solo books not making you a supporting cast member, Lois Lane and Jimmy Olsen are not included.
d. Since when did Damian become get a solo title? As a hardcore Damian fan I missed this. He's only appeared with Batman in a Batman title.
e. Your list is pretty shit. Boring and forgettable characters, the only two of those that go up to Alfred and Gordon are disqualified with point c of this post.