I'd rather see counterpoints to my arguments than blanket assertions

My apologies. I found myself convinced of these very points after reading the article, but I can see now how my words could come across as standoffish. No insult intended :)

Failure to perform the fait accompli means that options other than nuclear retaliation are possible.

My reading of both the text quoted and reality as presented, is that this line of thinking only applies when operating inside or very close to the opponents red lines. The next paragraph starts:

Avoiding this problem is why NATO is structured the way it is: promising a maximum response for any violation, however slight, of the territory of any member. The idea is to render the entire bloc immune to piecemeal maneuvers by putting all of it behind the red line (or at least letting the USSR think it is all behind the red line).

And Ukraine is not a member. NATO's red line is crystal clear. Ukraine is outside of it. Everyone made it very clear to Putin that they didn't want him to invade, and that they would impose "costs" on him if he did. But no one threatened to nuke him over it. 

NATO can clearly signal via way of action that it has no intention of threatening the existence of the Russian state.

Putin made it very clear on the day of the attack that he was threatening nukes to anyone who "interfered" in Ukraine, with his infamous "the consequences will be such as you have never seen in your entire history" -speech. NATO has been helping Ukraine by training their forces and supplying materiell for years before the invasion, and vowed to keep doing so. This can be considered "calling his bluff" to an extent, or as a piecemeal maneuver in it's own right. Yet they withdrew their personell from the country in the days and weeks leading up to the attack. Some have called Biden weak for doing that, essentially "clearing the way" for Putin by removing the tripwire force, and maybe he is. What is clear is that he didn't want for that bluff to be called. 

Sending NATO troops into Ukraine to engage Russian forces is a very clear escalation, that Putin has specifically warned against. If this were to happen, Putin would have every incentive to nuke them inside Ukraine, or worse. He might be bluffing. I wouldn't bet on it. 

"Red lines" aren't always geographical. Currently (it looks to me like) NATO's unambiguous red line is it's geographical border, while it is trying to establish some strategic ambiguity over use of chemical/biological weapons. This is going so-so, especially after the US's bluff was called in Syria with no consequences. Meanwhile (it looks to me like) Putin's unambiguous red line is Russia's geographical border, and he is trying very successfully and believably to assert a red line over any direct military intervention inside Ukraine, and less successfully over less direct help. Since he was deliberately unspecific in his threats, he can gracefully back down from the supply of weapons without loosing face. That does not mean he would back down from other more direct help, with the infamous Polish fighter jets toeing the line too close for comfort, so the US backed down on that one.

When Putin called that obvious bluff, it would have damaged the credibility and thus the deterrence

The start of the very same paragraph reads: 

The logic of deterrence – in particular the fact that it is both very high stakes and also based entirely on perception – explains why NATO and especially the United States took any direct military action off of the table quite loudly well before the conflict began. Saying that ‘all options are on the table’ – as the United States routinely does with Taiwan – would have been a fairly obvious bluff. When Putin called that obvious bluff, it would have damaged the credibility and thus the deterrence

Now, as for fait accompli:

Beaufre notes that for piecemeal maneuvers to be effective, they have to be presented as fait accompli – accomplished so quickly that anything but nuclear retaliation would arrive too late to do any good and of course nuclear retaliation would be pointless

I think the phrase "have to be" above is not to be taken as absolute. The same paragraph continues:

Thus Beaufre suggests that the piecemeal maneuver is best accomplished as a series of coups de main accomplished with fast moving armored, mechanized and airborne forces seizing control of the target country or region before anyone really knows what is happening. The attacking power can then present the maneuver as fait accompli and thus the new status quo that everyone has to accommodate; if successful, they have not only made gains but also moved everyone’s red lines, creating more freedom of action for further piecemeal maneuvers.

Everyone agrees that the maneuver "is best accomplished" if it can be performed quickly. Obviously Putin would be in a much stronger position if he would have been able to conquer Ukraine within a few days. Almost tautologically so. But considering how US Intelligence were consistently calling his shots days in advance during the weeks leading up to the invasion, Putin never managed to establish very much of a smokescreen for this operation, and thus I don't see this ever being presented as fait accompli to anyone, no matter how it would have turned out on the ground. Unlike his annexation of Crimea, where that tactic was much more successful.