Warhammer fantasy and 40K have a unique issue with deciding when they are serious or satire. Mostly spawned by disconnect from the writers building serious Tolkien-like detailed fantasy worlds, while the people making the game rules see the warhammer as silly. It is similar to Frank Miller always intending all stars Batman and Robin being a satire of how dark people writing superhero characters but DC marketed the book as serious.
From the aggressively on the nose real history parallels, names and locations, to entire cultures being straight up copied from real life, i think even the world builders understood that warhammer, both fantasy and 40k, was inherently built on a foundation of extreme cheese, with factions being flanderized equivalents of their real world counterparts. Kislev isnt merely inspired by eastern european countries and history, its literally "Slavobol.jpg", with polish hussars fighting alongside cumans and russian streltzys who ride around on bears, whilst worshipping a giant snow bear.
Bretonnia is a monty python skit, the empire is every meme about HRE, Elves and dwarves are cynical intepretations of Tolkien's optimistic versions etc.
But good writers and worldbuilders can take cheese and make serious stories out of it. its a testament to skilled writing when you can make a bizarre world serious and grounded. The emphasis on novels especially helped make 40k less into a meme, with the Horus heresy turning the civil war, which was at first just an excuse to print more space marine figurines, into a Illiad styled psuedo-mythological tragedy.
Did GW intend for it to be satire or not? no idea. they just wanted to make money, and left the rest up to creatives.
Warhammer 40K is like Judge Dredd. Judge Dredd is supposed to be a British far-left satire on American gun control, America, anti-police and anti-police brutality. But the general public ended up loving judge Dredd instead of hating him. Actual ommunists thought accused Judge Dredd of being a pro-fascist comic. British nationalists accused judge Dredd of being pro-American propaganda. They made Judge Dredd villains too evil. Any point of police brutality is lost when Dredd curbs stumping a cannibal gang leader running a child human trafficking ring. Warhammer 40K taken seriously is an anti-religious story where hell is 100% proven and mortal lives at risk from chaos gods.
From what i've read, whilst it was definitely meant as an exaggeration of policing it initially started out mostly as just action comic, albeit with slight critiques aimed at authoritarianism.
It was only later when the popularity of the comics grew and people (young guys in particular) began to venerate dredd, not merely loving the character, that the original authors turned up dial on the satire and criticisms, especially with the "democracy" story-line which all but turned Dredd into a villain.
But as you said, attempts to criticize authoritarianism and xenophobia falls flat when the bad guys actually warrant an extreme treatment.
But where warhammer, mostly 40k, differs is that there is a level of romantic deification of the in-universe religion and factions. Especially by people who extrapolate the Imperial truth to include a sort of traditional christian bent against the, by proxy, degenerate and loose nihilistic ruinous powers, which is very appealing to a ton of religious people. Obviously no one is switching from catholicism to unironically become a member of the Imperial cult, but for a lot of people a setting where not-quite-christianity is enforced as a force for mostly good against commie-aliens, low-IQ orks and futanari demons might have a certain degree of appeal.
Even the authors, when they try to apply a critical lens, do so through a sense of nuance. Zealots are brave and puritans are vigilant etc.
just compare that to most other "not-quite-christianity" examples in fantasy, and most of them are either vague and poorly defined, or just thinly veiled critiques of Christianity.
