The cited example is a misrepresentation of the original
The Bounding into Comics web article quotes "current WotC designer Jason Tondro" as saying in "the preface to the game’s recently published history book, Dungeons & Dragons – the Making of Original D&D: 1970-1977":
“The cultural appropriation of original D&D ranges from the bewildering (like naming every 6th-level cleric a ‘lama’) to the staggering; Gods, Demigods, and Heroes (not reprinted in this book) includes game statistics for sacred figures revered by more than a billion people around the world. Were players expected to fight Vishnu, one of the principal deities of Hinduism, kill him, and loot his ‘Plus 3 sword of demon slaying’?”
Taking this quote at face value (I haven't read the actual preface), the answer is clearly, No, this was not the expectation.
Were PCs supposed to fight gods? No.
Gods, Demigods, and Heroes (1976) was OD&D Supplement IV, by Robert Kuntz and James Ward (and not, as it happens, by Gary Gygax). The only explanatory text indicating how it was to be used comes in the Foreword by Tim Kask, where he says:
What the authors have done in this volume is to attempt to set down guidelines that will enable you to incorporate a number of various mythologies into your game/campaign.
By 'incorporate mythologies', Kask means to say that here are real world divine beings described with OD&D stats, the purpose of which is to enrich the campaign background by providing gods for the PC's and their foes to worship. The stats argue for relative power level among the gods, which will be reflected in the levels of their clergy and the numbers of their adherents in the campaign world, but they are not explicitly set up as combat challenges for the PCs. Indeed, Kask later says:
This volume is something else, also: our last attempt to reach the "Monty Hall" DM's. Perhaps now some of the 'giveaway' campaigns will look as foolish as they truly are. This is our last attempt to delineate the absurdity of 40+ level characters. When Odin, the All-Father has only(?) 300 hit points, who can take a 44th level Lord seriously?
In other words, if the PC's are at the level to actually fight these gods, then there is something "wrong" with your campaign.
In first edition, this work was updated to Deities and Demigods by the same authors, with entries largely reprinted from the original. The Foreword, this time by Gary Gygax, repeats that the purpose of the work was to bring a grounding of religion and alignment into the background of the game, most especially for players of the cleric class. Gygax makes a slightly different second point, however. He does not say that it is 'foolish' for PCs to rise to the level of gods - but that if and when they do, they should be treated as gods and no longer as PCs, that is, removed from play.
Were they expected to fight Vishnu, specifically? No.
Gods, Demigods, and Heroes contains beings from ten pantheons, starting with Ancient Egypt (which is represented on the cover) and continuing with what is variously called the 'Gods of India' but also 'Hindu Mythology', (Ancient) Greek, Celtic, Norse, Finnish, Hyborea, Melnibone, "Mexican and Central American Indian", and "Eastern". Among the Hindu gods, Vishnu is just one of eighteen divine beings. So, there is no directive to fight Vishnu specifically (nor do I think that is what Tondro was implying). From the description of Vishnu, however, it is unclear how PCs would even be able to fight, since:
His primary power is the ability to make any creature or being unable to commit violence of any type within 30 yards of his mind (no saving throw applicable). Vishnu can also make a double strength prismatic wall, as per Greyhawk, shapechange. and teleport.
Thus as presented, Vishnu could simply will any PCs close to him to not fight, use a prismatic shield to protect himself from ranged attacks, and then teleport away.
If Tondro's hyperbolic thesis is that all of the beings presented in Gods, Demigods, and Heroes existed as creatures for the PCs to slay and loot, he picked a particularly bad example.
So, to Tondro's rhetorical question, 'were PC's expected to fight Vishnu?' the answer is clearly No, they were not.
But did they anyway? Yes.
Yes, of course. Even though the explicit instruction in both works was that they were not designed with the purpose of PCs fighting gods, they nevertheless presented gods with defined statistics, thus making such a thing possible within the rules of the game. Most old school gamers know of someone's campaign in which the PCs fought gods, even if they did not do so themselves. In his 1991 book Heroic Worlds, Lawrence Schick says of DDG: "Unfortunately, the book is usually used merely as a sort of Monster Manual that describes very high-powered monsters. This usage is encouraged by the book's format, which emphasizes the gods' physical abilities over their religious significance." And RPG historian Stu Horvath in his 2023 book Monsters, Aliens, and Holes in the Ground apparently "noted by listing the deities' hit points and other game statistics, the book tacitly encouraged high-level power gamers to take on the deities in combat."
Ultimately, it was not the explicit design intent of such works to encourage PCs to fight gods, but it did enable it. Tondro's question (if accurately quoted) is self-serving and probably deliberately disingenuous. Was assigning statistics to real-world religious figures sacrilegious? Sure, but no more so than a game in which those figures already play a role that serves an explicitly fictitious narrative. And no more so than calling a collection of divine beings still worshipped by living cultures a "mythology". But was it "staggering cultural appropriation"? That strikes me as protesting a bit too much from the current IP holder and beneficiary of the early game's legacy. One could also note that the 5e game explicitly includes the Norse gods, divine beings worshipped by real world contemporary neopagans, and Tondro doesn't seem to be clutching his pearls about that.