No, Ibranyi actually highlights the problems with sedevacantism. Of course most sedevacantists will disavow Ibranyi and denounce him as a nutjob.
But WHY is Ibranyi a nutjob? That kind of consideration is EXACTLY what led me to backtrack away from sedevacantism. I ran into a slightly less nutty person who believed that Pius XII was not a legitimate pope. Most sedevacantists would reject that position. OK, fine.
But the important thing is to understand WHY rejecting Pius XII is wrong. Based on what PRINCIPLE would it not be allowed to reject a Pius XII? It's not enough to say that you can't reject Pius XII but can reject Paul VI. You have to explain why it's OK in the case of Paul VI but NOT OK in the case of Pius XII. What is the PRINCIPLE involved? Only thing I ever hear is that Paul VI was a heretic but Pius XII was not. But that's all based on the fact that you simply say so. Those people who reject Pius XII are just as certain that he was a heretic as you are that Paul VI was a heretic.
When I have time this evening, I'll explain how it is that I came from considerations like this to investigating and coming to understand that principles that led to my sede-doubtist position.
It's exactly the kindof extreme applications of sedevacantism (such as exemplified by Ibranyi) that led to me rethinking sedevacantism.