WARNING: The following contains spoilers for What If...? Season 1, Episode 8, "What If... Ultron Won?," streaming now on Disney+.
The true Age of Ultron is at hand as the most recent episode of What If...? details how the Infinity Stone-empowered automaton rampages throughout the multiverse, driven by passionless, pure nihilism. Introduced in Episode 7, "What If...Thor Was an Only Child?," the penultimate entry of the first season shows how Ultron, now inhabiting Vision's body as he originally intended, nonchalantly uses the Mind Stone to cut Thanos in half, takes possession of the other five Infinity Stones and goes about successfully destroying his home universe.
The breathtakingly casual manner in which the Mad Titan is dispatched has inspired a deeper reflection among fans on the Mind Stone and Vision himself. All things being equal, if Vision had an opportunity to face Thanos during Avengers: Infinity War, could he have beaten the villain the same way and prevented the snap? There are a few key facts supplied by the Marvel Cinematic Universe to keep in mind.
In Guardians of the Galaxy, Korath the Pursuer refers to Thanos as the most powerful being in the universe. This establishes for the audience the immense risk Ronan the Accuser is taking by betraying the lone Titan and sets the expectations for how this rarely glimpsed villain will eventually dismantle the known universe. His subsequent appearance in Infinity War lives up to the dire warnings and dread-filled mystery. Disney+, however, has tempered Thanos' power levels on more than one occasion.
In "What If... Zombies?!" Thanos is in Wakanda brandishing a gauntlet with a handful of all-powerful ingots, zombified somehow. The Hulk's invulnerability seems to stave off infection but Thanos is vulnerable in some undisclosed way. In "What If... T'Challa Became Star-Lord?" Thanos is bested by a pair of his former lieutenants. Proxima Midnight and her husband Corvus Glaive are formidable, but they hardly seem like a match for the same Thanos Korath described as the most powerful being in the universe, even before the acquisition of any Infinity Stones. As far as these six compressed cosmic singularities are concerned, Loki treats them as inconsequential baubles. TVA agents use them as paperweights and Miss Minutes offers them to Loki and Sylvie as a bribe to allow the TVA's continued policing of the multiverse.
The final blow to the Titan's wilting stature is Ultron slicing him from head to nip with the Mind Stone before he can react in any way. It takes Ultron longer to vaporize the knuckles of the gauntlet and free the Stones from their housings than it did to kill Thanos. Repeated disrespectful displays aside, Ultron seems to intuit the powers of the Stones very quickly. This may be how the Stones work in the MCU. The only people who have ever wielded it, Thanos, Smart Hulk and Tony Stark, were already aware of them and their power, so it is unclear what knowledge the entire collection of Stones may impart to their bearer.
That said, Ultron is part Tony Stark, part Bruce Banner and part the Mind Stone itself, and the proportions are likely nowhere near equal, as evidenced by Ultron's personality. He doesn't seem to carry anywhere near the same degree of animus towards Banner as it does Stark, likely because more of the inventive mechanisms that power Ultron are due more largely to Stark than Banner. When the two scientists observed the Mind Stone's internal architecture, it resembled a sentient computer, at least according to their ability to comprehend what they were looking at, which existed before they meddled. Perhaps this pure incarnation of the Stone, made synthetic flesh, was more capable of unlocking its powers than the Jarvis-driven entity that became Vision in the MCU Sacred Timeline. In Captain America: Civil War, Vision admits to Wanda that he isn't even sure what the Mind Stone is and it stands to reason that What If...?'s Ultron might have a more intimate understanding, even if it is only on a subconscious level.
While it seems oddly irreverent to manhandle Thanos' infamy as arch-villain number one, it also stands to reason that this version of Ultron would be more adept with the Mind Stone and its powers. This alternate has an argument, and perhaps the Thanos of its universe was somehow inherently weaker than the core MCU's, but there doesn't seem to be any scenario where the Sacred Timeline's Vision could ever defeat its Thanos, who had already harnessed five of the six Infinity Stones.
The final episode of What If...? airs Wednesday, October 6th on Disney+.