The pope question, as it were, is but a distraction/red herring.

The real problem is that -- regardless of who is or is not the legitimate head of the society that purports to be the Catholic Church --  a society that is supposed to be one, holy, catholic, and apostolic, the spotless Bride of Christ, without blemish and the single, solitary means of sanctification and salvation is, and has been for several decades, naught but a source of confusion, spiritual destruction, endless scandal, etc.  Whether he is or is not legitimate, solving that issue doesn't alter the cold, hard, unspeakably-sad fact that what used to be Holy Mother Church has, to all appearances, become an absolutely shameless harlot leading millions to eternal misery.

Address that.

My view is so obviously correct that...

On the contrary this supports sedevacantism.

Yes, it most certainly does … unless you think there’s nothing all that wrong with V2.  Stubborn, however, constantly begs the question that the V2 papal claimants are popes and thus engages in circular reasoning.  For some reason his brain can’t break out of this illogical cycle.  It’s bizarre, really, and speaks to some psychological issue.

Basically, his brain can’t / won’t grasp what’s known as modo tollentis logical reasoning.

If A leads to B, then not B means not A.  But since he refuses to let go of A, this doesn’t register.

Stubborn, the way your brain works (or, rather, does not work) is what's amazing.

I'm sure you can find a basic logic class online.  I highly recommend it.

Given the MAJOR premise above from Msgr. Fenton that a Pope cannot teach substantial error to the Church, there are only two possibilities, outside of rejecting Fenton's premise altogether.

There are two basic logical forms, 1) modo ponentis (MP) and 2) modo tollentis (MT).

MP goes like this.
MAJOR:  If A, then B.
MINOR:  A.
CONCLUSION:  B

MT goes like this.
MAJOR:  If A, then B.
MINOR: NOT B.
CONCLUSION:  NOT A

With regard to the issue at hand, the conservative Conciliars adopt the MP reasoning.  SVs adopt the MT reasoning.  Most R&R simply dey the MAJOR.

Let's try a simple example.

MP (modo ponentis)
MAJOR:  If a polygon is a triangle, it has 3 sides.
MINOR:  This polygon is a triangle.
CONCLUSION.  This polygon has 3 sides.

MT (modo tollentis)
MAJOR:  If a polygon is a triangle, it has 3 sides.
MINOR:  This polygon has 4 sides.
CONCLUSION:  This polygon is not a triangle.

MAJOR:  Popes cannot teach grave error to the Church. [oversimplification of Fenton for brevity]
=
MAJOR:  If someone is the Pope, he cannot teach grave error to the Church.

So, MP (adopted by conservative Conciliars).
MAJOR:  If someone is the Pope, he cannot teach grave error to the Church.
MINOR:  Paul VI was Pope.
CONCLUSION:  Paul VI did not teach grave error to the Church.

So, MT (adopted by sedevacantists).
MAJOR:  If someone is the Pope, he cannot teach grave error to the Church.
MINOR:  Paul VI taught grave error to the Church.
CONCLUSION:  Paul VI was not the pope.

In order to reject SVism, you have to either deny the Minor (as the Conciliars do), namely, that Paul VI taught grave error to the Church, or deny the Major (Fenton's position), which is what most R&R do.  But if you accept both the MAJOR and the MINOR, the the conclusion necessarily follows that Paul VI was not the pope.

Correct.  You deny the MAJOR.  But if you accept the MAJOR, then you have to either deny that V2 taught error to the Church or have to conclude that Paul VI was not the pope (as per the above examples).

What Msgr. Fenton was teaching precisely rejects your proposition above, and that's the entire point.

I think you’re a wee bit confused. The major is that they *can’t* teach substantial error

Fr. Chazal's position of Sedeimpoundism is merely a different version of Sedeprivationism. If Fr. Chazal ever publicly stated that he was a dyed-in-the-wool Sedevacantist, then he would obviously lose a lot of parishioners (some of whom may even demand his resignation or transfer).