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This is false.

This response proves my point.  You've compressed the entire syllogism into a single proposition.  But you're really only speaking of the MAJOR in the SV proposition (with which I wholeheartedly agree, BTW).  I agree this this statement above is de fide.  But then where is the rest of the argument?

MAJOR:  The Church cannot teach heresy in her official capacity and magisterium to the universal faithful.  (agreed, de fide)
MINOR:  The Conciliar Church has taught heresy in an official capacity and in its magisterium.
CONCLUSION:  Conciliar Church is not the Catholic Church.

I actually agree with this conclusion and have argued this myself.  But here's the problem.

Look at the MINOR (which you've lost sight of due to your compression of the entire argument into it being a restatement of the Major alone).  When did the Church teach this?  Never, since the Church has been in eclipse since this whole thing started.  We have arrived at this conclusion based on our private judgment.

Because the MINOR only has fallible private judgment behind it, the conclusion also depends on fallible and non-authoritative private judgment.

Ah, but the SV would respond:  Vatican II was condemned by past Magisterium.  No it wasn't, not explicitly.  It is your contention and argument that the propositions in Vatican II contradict previous Magisterium, but the Church has not officially ruled on whether that was in fact the case.  I've seen decent and plausible attempts to argue that the teachings of V2 can be interpreted in a way that's consistent with the previous Magisterium.  I do not agree with that, but this is MY OPINION.  I cannot bind consciences.  I have no authority.  Neither do you.

So you call this simple because you OVER-simplify it, compressing the entire argument into the Major alone.  And then because the Major is in fact de fide, you falsely believe that the conclusion is also.

THIS here is the chief error of dogmatic SVism.