Mac,
I hope that answer your question about the legitimacy of the Novus Ordo and what sense it is to be understood by the SSPX and the Superior General. '
As to your specific question. - For my part no I don't see any heresy in the doctrinal declarations of the Superior General or the SSPX. If you want to point them out to me, I would be glad to discuss them with you.
As for his private letter to his fellow bishops, that was private correspondence. I can respect that fact, even if others can't. If Bp. Williamson or anyone else for that matter wants to write the Superior General a public letter and make it public, well good for him, but if such a person can't respect private correspondence, well, what can I say for such a one?
As a good priest recently pointed out to me, anything other than heresy does not give anyone the right to rebel against his superiors, otherwise we introduce the rule of anarchy into the Church. Never in the history of the Church has the Church praised rebellion when there hasn't been sufficient grounds for. Contrary to this, the Church has always condemn all such rebellions/schisms etc as being contrary to will God and His Church.
Just read the lives of the saints, many a time their superiors were mistaken, and did things to them which were not just and for all that they did not rebel but remain humble and faithful, for unless it is a question against the faith, obedience is called for. - Apply the same logic in your own home. It isn't that difficult.
No one in the resistance would say that they have always agreed with everything that Bp. Williamson has ever written or done, and yet for all that when he was a superior in the SSPX no one would have held that just because someone disagreed with something he has said/written that it is sufficient grounds for rebellion. To me it seems that the resistance isn't able to see beyond the personal dislike for Bp. Fellay, and this becoming clearer in the insulting way they speak about him.
Be it far from anyone to insult clergy in such a way, SSPX or otherwise. The mocking tone in which some here even speak about the Pope is all out of place. He still has a dignity which is far beyond that of any one of us here. You can't embrace the Novus Ordo attitude towards authority, just because you may not agree with them. Two wrongs don't make a right.