In What if…? Episode 8, we see an alternate universe where the Avengers failed to steal the cradle from Ultron and, instead of Vision being born, Ultron was successfully able to upload his consciousness to the Android body, defeat most of the Avengers, and ultimately succeed in his plan to “pacify” Earth.
After Ultron is the ultimate force left on Earth, Thanos shows up with the Infinity Gauntlet bearing all the other Infinity Stones and this is where Ultron discovers that there are other stones than the Mind Stone, effortlessly kills Thanos and gets the stones for himself.
As far as I know, Ultron’s power should be similar to Vision’s now that he inhabits the same Android body that would become Vision in the main universe. This begs the question: why was he able to defeat Thanos so effortlessly when Vision seemed to be the Avenger most vulnerable to both Thanos and the Black Order in Infinity War?