This is an especially big problem with a badly defined word like this,
Edit: I wrote this comment, clicked through, and of course Eco is the first writer referenced.
The original article also does not really fit the Socialist Russia that much. It was seeking world domination and did not minded to start a war, but that is the thing - it was concerned more with reality of winning then with appearance of strength for aesthetic purposes. It had own machismo, it had disdain to intellectualism, but both did in fact limited its capabilities.
It's a bit light on rigor than I hoped when I saw the title. It describes 3 fascist or near-fascist states that lost in recent history: Germany, Italy, Franco's Spain. But I wanted to know if Rome under Julius Caesar would be considered fascist? Alexander of Macedon? And also non-western states as well.
IMO it is less about fascism but wars of conquests that are more likely to be doomed to fail. Maybe fascism is a requirement for desires of conquest so they are tightly related.
For conquest to succeed it must be quick and overwhelming. Otherwise it becomes a war of attrition against an enemy that has way better motivation than your army. But also, even if you have a decisive victory, it is almost impossible to stop at just one victory because the war machine will be thirsty for more and your entire economy will be dependent on it, so you have to keep going until total failure.
The king's powers were not unchecked. People had human rights by custom and law (Magna Carter, for example), parliament controlled taxation, aristocrats had a great deal of power, the Church had a lot of power.
Nowhere near democracy, but a very different system from an unchecked dictatorship.
Edit to add: this was the system from which modern democracy slowly evolved.
I don't think he makes the case that an unwise focus on the signifiers rather than the reality of military strength primarily explains the defeat of either Nazi Germany or Mussolini's Italy in WWII. Did the Nazis and Italian fascists actually do this to a greater extent than any of the other participants of the war? Certainly every major participant in WWII had propaganda about how good its army was, including the United States and Britain ("videos" is anachronistic for the time period, but there's plenty of American WWII military propaganda that was originally a black and white filmstrip that's been digitized on YouTube). And every major participant in the war had a great deal of actual, non-fake, military strength. Fascist Italy was certainly a junior partner to the Nazis, but Nazi Germany was primarily defeated in the incredibly bloody Eastern Front, mostly by the armies of the Soviet Union expending huge amounts of blood and treasure in order to do it. It was not a trivial victory, nor I think an inevitable one.
The Soviet Union was an officially state socialist country, an ideology that saw itself as directly opposed to fascism. Particularly under Stalin, it can hardly be described as a country "willing to engage in potentially embarrassing self-study and soul-searching" - indeed Stalin's purges of large fractions of Soviet society in the 1930s, including the military, are a commonly-cited reason why the Nazis had so much success in the initial phases of the invasion of the Soviet Union.
Of course every allied power in the war was being supplied materially by the United States, which had an extremely favorable geographical position and cultural disposition to produce material goods. Maybe whichever side in the war the US supported would've won. Or maybe some third thing would've happened, WWII is one of the most well-studied conflicts in human history (and for good reason, it was a pretty important one!), there's lots of people with lots of ideas out there about how it could've gone differently than it did.
Looking beyond Nazi Germany and Fascist Italy to other countries also weakens the argument. Let's say for the sake of argument that Franco's Spain counts as fascist. Then the fascists won the civil war, avoided fighting in WWII at all and thereby being destroyed like Nazi Germany was (although I think this was also not a foregone conclusion, and had more to do with the geopolitical calculus of the Allied Powers than anything Spain itself did at the time), and ended up surviving until Franco died of heart failure at the age of 82. At which point the country had a series of contentious-but-ultimately-peaceful political reforms resulting in its modern constitutional monarchy. This doesn't really sound like a narrative where a focus on the trappings rather than the reality of military ability resulted in a fascist nation fighting an aggressive war of choice and then losing! This might've just been Hitler specifically! (And it's not like that was the first time Germany did this sort of thing - was Kaiser Wilhelm II fascist? What about Otto von Bismark - the Franco-Prussian war went fairly well for Prussia and fairly badly for Napoleon III's France, actually, although maybe this is getting too far back in the past for labels like "fascist" to be useful).
If Salazar's Portugal was fascist, then doesn't the fact that it avoided aggressive war imply that fighting (and losing) aggressive wars isn't very diagnostic of fascism? If the fact that it lost its overseas colonial empire constituted a military failure of fascism, then what are we to make of the fact that so did Britain and France at roughly the same time and for the same set of reasons? Was France suffering from fascist overconfidence in its military when it failed to win the First Indochina War? Immediately after having been successfully conquered by Nazi Germany for a few years and then successfully expelling them along with the other allied powers in exactly the same war that Nazi Germany lost as thoroughly and completely as it is possible to lose a war?
Saddam Hussein's Iraq is also a poor example, because while it was a cult-of-personality dictatorship and there was definitely a great deal of the trappings of military strength rather than actual military strength - Hussein did not tolerate his subordinates bluntly telling him the actual truth on the ground - Iraq didn't actually lose his war of choice against Kuwait because of anything Kuwait did. He lost it because the United States, in its capacity as a global superpower, decided that it wasn't going to tolerate Iraq invading Kuwait and more-or-less unilaterally - and easily - destroyed Iraq's army in the First Gulf War. And of course in the Second Gulf War Iraq didn't really do anything, which is why so many people thought it was immoral - indeed, fascist! - for the US to wage another aggressive war of choice against Iraq, again more-or-less unilaterally, and again easily destroy Iraq's army, depose Saddam Hussein, set up a puppet government that tried and executed him, and basically run the country for another decade or so until the US got tired of it. I don't think this says anything about fascism or near-fascism, I think this says that the United States is World Police (you know, like that movie the South Park guys made, at the time).
I think the actual point of this essay is that the author is operating in a framework where he wants to compare his domestic political opponents to Nazi Germany - because that's a metaphorical framework that has been in play in liberal democracies since they were actually fighting WWII against the actual Nazis - and because he's a historian who focuses a lot on warfare, he wants to do this by arguing that actual fascist governments (both of them) were bad at war even though they had the trappings of being good at war. So therefore his domestic political opponents, who he calls fascists, must also be foolish blowhards who are actually weak and pathetic.
You don't write something like "Put bluntly, fascism is a loser’s ideology, a smothering emotional safety blanket for deeply insecure and broken people (mostly men), which only makes their problems worse until it destroys them and everyone around them." if you're trying to actually understand why various types of government performed the way they did in actual wars - you write this if you're actually talking about people in your liberal democracy who you don't like and are trying to insult. And you write "(mostly men)" if you're operating from a framework which treats masculinity as inherently suspect, which is a contemporary domestic-politics political signifier, rather than something that was relevant to explaining why the Soviet Union ultimately militarily defeated Nazi Germany.