I am in disagreement with you here. His analysis is not philosophically coherent and his argument is therefore invalid.
The fact of Derksen's recent conversion to sedevacantism--this article was written two years ago--in no way invalidates the cogent argument he presents.
I agree with you that the mere fact of his sedevacantism does not mean that his arguments are automatically wrong.
This is why I mentioned his philosophical incoherence as a reason to disregard Maximilian's estimation of his views.
By the way, thank you for describing his position so accurately and pithily as a "conversion to sedevacantism."
Sedevacantism is indeed a separate, non-Catholic religion and one must effectively convert from Catholicism in order to become a sedevacantist.
On the contrary, his argument is brilliant. The Pope is a humanist--all his writings, his speeches, his actions, show this beyond a shadow of a doubt. It explains Assisi I and II--which are a scandal to the rest of us and a violation of the First Commandment. This Pontiff's grounding is not in Thomistic realism but in the methodologies of personalism and phenomenology--where truth itself is a shifting thing, according to one's experience of it.