"Sedevacantism is heresy" is like "God of the Gaps is fallacy"

The idea behind "Sedevacantism is heresy" is "Sedevacantism implies the gates of Hell did prevail" which would indeed be heresy.

But the sedevacantists do not admit the position implied the gates of Hell prevailed.*

And Theists do not admit an argument from Design being an argument from ignorance about the naturalistic and as yet unknown naturalistic cause of design like features in the world.

So, what do the above sentences have in common? Is "Sedevacantism is heresy" like "God of the Gaps is fallacy"? Yes, both are the fallacy of straw man./HGL

* Perhaps especially not those of us who are Orthopapist.