Well, Cathedra Unitatis, to give him credit, did take notice of the post put up by Perry taking a cite from the 5th Ecumenical Council. The discussion there is well underway now, with about 45 responses at the time of this post.
Relative to papal claims, why is this important?
In summary, because it establishes, unequivocally, the standard of collegiality among the bishops. And it presents the Roman Pope Vigilius as issuing a dogmatic decree, retracting it, and submitting to the decision of the council.