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Whoever this John Farrel is, he's absolutely right on target.

In the "Allocution to Midwives", Pius XII cites Pius XI but actually leaves out the crucial part where Pius XI in Casi Conubii effectively condemned NFP.

Pius XI taught that TWO things are required for the licitness of the marital act --

1) that the inherent power of the marital act be preserved (vs. artificial birth control)
AND
2) that the primary end can never be subordinated to the secondary

Pius XI LEFT OUT the second condition, citing only the first.  It's this second condition that precludes the licitness of NFP.  Why doesn't he cite that?

You can clearly tell in the language of this long, rambling speech that Pius XII was doing nothing more than speculating, and that he was not teaching anything authoritative (as opposed to those who claim that this authoritatively decides the matter).

See, with Pius XII, he didn't actively impose anything harmful, but he "opened the door" (and later the floodgates) to both NFP as Catholic Birth Control and also to Evolution.  Simlar to NFP, Pius XII never taught that it was acceptable, falling short of that, just "permitted' Catholics to debate the subject.

Pius XII's papacy was, alas, THE watershed that led directly to Vatican II and all its evils.  Pius XII --

1) opened the door to Evolution
2) opened the door to NFP
3) opened the door to Liturgical Experimentation (first appointed to Bugnini to begin the experimentation, push out the "reformed" Holy Week Rites, Psalter, New Vulgate translation, and permitted abominations like "The Mass of the Future"
4) failed to consecrate Russia to the Immaculate Heart of Mary
5) consecrated nearly every bishop who would go on to bring us the glories of Vatican II
6) allowed the heresiarch Cushing to persecute Father Leonard Feeney for simply reiterating defined Church dogma, thus allowing THE core error (EENS-denial, the resulting non-Catholic ecclesiology that would manifest itself explicitly at Vatican II, and rampant religious indifferentism) to fester and gain the upper hand
7) failed to curtail or curb the spread of Modernism in any way

Pius XII was consecrated a bishop on the exact day (May 13, 1917) that Our Lady appeared at Fatima.  He also claimed to have seen the miracle of the sun in the Vatican Gardens.  So it was said that he was "The Fatima Pope".

Well, probably so, but only in a tragic sense.  Could he have been the one depicted in the released part of the Secret who led the faithful to the slaughter?  He was the last Pope who by consecrating Russia could have prevented Vatican II, but he refused to do so.  Our Lady could very well have appeared on the exact day of his episcopal consecration to indicate that he was the last Pope who could prevent the evils of Vatican II by heeding her requested and consecrating Russia, to prevent the evils she came to warn about when the Jєωs, Communists, and Masons would take over the visible structures of the Church.

OP, you may find this previous discussion on the matter useful: https://www.cathinfo.com/crisis-in-the-church useful/article-on-nfp-from-introiboadaltaredei/

The above-linked thread references even previous threads that you may also find useful. 

Whoever this John Farrel is, he's absolutely right on target.

In the "Allocution to Midwives", Pius XII cites Pius XI but actually leaves out the crucial part where Pius XI in Casi Conubii effectively condemned NFP.

Pius XI taught that TWO things are required for the licitness of the marital act --

1) that the inherent power of the marital act be preserved (vs. artificial birth control)
AND
2) that the primary end can never be subordinated to the secondary

Pius XI LEFT OUT the second condition, citing only the first.  It's this second condition that precludes the licitness of NFP.  Why doesn't he cite that?

.
I believe you are wrong to make the distinction you are making. Pius XI teaches that if the intrinsic nature of the act is preserved, the ends are necessarily subordinated. We have argued this specific point about once a year since 2018 or so. Do you have any new arguments or evidence to back up this distinction?