No ...

No ... and now we have an another armchair Canonist (where did you get your degree?)

• Canon 188.4: This canon establishes the principle of "tacit resignation" for a cleric. It states that "any office becomes vacant upon the fact and without any declaration by tacit resignation recognized by the law itself if a cleric... publicly defects from the Catholic faith". This means that the cleric would lose his office automatically upon committing a public act of heresy.
• Canon 1324: This canon (and the closely related Canon 1325) defined heresy as the "stubborn denial" of a truth proposed by the Church as divinely revealed.
• Canon 2200: This canon explains that in the external forum (meaning, publicly), the intent to commit a crime (in this case, the pertinacity required for heresy) is presumed from the external violation of the law.
• Canon 2314: This canon specified the penalties for the crime of heresy, including automatic excommunication. For a cleric, this was compounded by the tacit resignation of office mentioned in Canon 188.4.

• Denunciation: A layperson who became aware of a cleric's public heresy would bring a denunciation to the cleric's bishop or other appropriate ecclesiastical superior.
• Investigation: The superior would investigate the claim to determine if the public defection had occurred.
• Automatic Vacancy: If the cleric's defection was judged to be public and pertinacious (stubborn), Canon 188.4 would apply. The cleric's office would be considered vacant by the law itself, effective from the moment he committed the heretical act.
• Declaratory Sentence: While the loss of office was automatic, a "declaratory sentence" might be issued by the Church. This sentence did not impose the penalty but confirmed that it had already been incurred. This was necessary to make the vacancy official for legal purposes and to allow for the appointment of a new office holder.

Your problem is that you're reducing heresy to sin alone.  No, it's more than that.  The sin of heresy is 1) a violation of the 10 commandments (i.e. a sin).  2) it's also a HUMAN violation of church law/canon law.

A heretic rejects the faith, so no, they are no longer a member.  And no, they cannot simply go to confession.  Because heresy is a two-fold violation - 1) sin against God, 2) violation of canon law.

Not sure what your point is here, but to answer your question, it does not say that the Church held to that, it says that the Montanists heretics held to that. It says that the Church authorities (correctly) held the contrary view. 

• External act required: The heresy must be externalized, meaning it is expressed through words or actions. Simply holding a private, erroneous belief does not constitute a canonical crime.
• Formal heresy is distinct: MacKenzie differentiates between formal and material heretics. A heretic who denies the faith due to "inculpable ignorance" might not incur the canonical crime. However, a formal heretic, who knowingly and persistently denies a defined doctrine, is subject to penal consequences.
• Automatic excommunication: The commission of a formal, external act of heresy incurs an automatic (ipso facto) excommunication. This penalty immediately severs the
• heretic's legal membership in the Church. MacKenzie notes that this is a self-imposed act of separation, rather than one explicitly declared by a juridical authority.
• No longer part of the body: By separating themselves from the Church's faith and unity, heretics also separate themselves from the visible body of the Church. MacKenzie underscores the severity of heresy as an offense against the faith itself, which strikes at the very foundation of the Church's unity.

There is no such thing as reducing an offense against God to a sin alone. One mortal sin is the worst thing that could ever enter creation. 
 
What you say about heresy is also said for adultery, abortion, willful murder, sodomy, and so on.

Heresy is a sin, it's the worst sin of all the sins. But that's what it is, a sin.

Then they can never obtain absolution without first taking all the classes meant for catechumens.

If they cannot simply go to confession, then why, in the traditional formula of absolution in the Sacrament of Penance as posted below, is there is a general absolution from the censures of the Church?

"...May our Lord Jesus Christ absolve you: and I, by His authority, absolve you from every bond of excommunication, suspension, and interdict, in so far as I am able and you are needful. Next, I absolve you from your sins, in the Name of the Father, and of the Son, and of the Holy Ghost. Amen

Not sure what your point is here, but to answer your question, it does not say that the Church held to that, it says that the Montanists heretics held to that. It says that the Church authorities (correctly) held the contrary view. 

 Are you sure you are reading that right?

"The Montanists, at this time and later, held that apostates could not be absolved from their sin nor restored to membership in the Church, no matter how sincere their repentance. Church authorities of orthodox faith held the contrary view , but were concerned to regulate the manner of reconciliation." 

The Church's view was the "contrary" view to that of the heretics.

The heretics believed that those who apostasized COULD NOT regain membership.

The Church held the contrary view that they COULD regain membership.

Thus, how could they regain what they never lost - if your "once a member always a member" thesis was true.

capisce? 

Yes, Stubborn read it wrong. 

MacKenzie's analysis, which reflects the provisions of the 1917 Code of Canon Law, emphasizes several key points regarding a heretic's loss of membership:

• No longer part of the body: By separating themselves from the Church's faith and unity, heretics also separate themselves from the visible body of the Church. MacKenzie underscores the severity of heresy as an offense against the faith itself, which strikes at the very foundation of the Church's unity.

Really?

So this is wrong?:

What does Rev. Eric MacKenzie teach in the 1932 Canon Law Dissertation, "The Delict of Heresy" about how the Church views heretics in terms of their membership status?

In his 1932 dissertation?The Delict of Heresy in its Commission, Penalization, Absolution, Rev. Eric MacKenzie teaches that a baptized person who becomes a formal, manifest heretic automatically ceases to be a member of the Catholic Church. He bases this canonical and theological view on the principle that the act of obstinately denying or doubting a defined truth of the faith separates the heretic from the body of the Church.

Can you quote a pre-Vatican II theologian that teaches that, (without interpolating your own interpretation), I mean just a verbatim quote that was a source acknowledged to be theologically credible prior to Vatican II?

I'm not the one reading it wrong.

The Montanists are the heretics. The heretics held that apostates 1) could not be absolved from their sin 2) nor restored to membership in the Church.

The Church authorities  held the contrary view. Which means 1) Apostates can be absolved and 2) ipso facto they were already members of the Church.

The Church can never absolve non-members, the Church can only absolve members.  It's really not the least bit complicated.