Many of those names you brought up are debateable in terms of success when you consider the quality of team/coach that he played with/for: Orton, TJax, Vick (he's over the hill, no way you can say he's better now), Hill, Flynn, & Cassel (ya kiddin? He played for the mad genius with the "insert any player here and be successful" system).
Hasselback falls under the category of very close to retirement and not a good long-term backup.
Not makin very good arguments here.
Fitz has more than the equivalent of 3 full season under his belt as a starter in the NFL and is in the "prime" of his career in terms of age.
I don't really see how Henne, Kolb, or Anderson are better backups.