That should be taken into account too, sure, but so should everything else I mentioned. In the lead up to MoS, the marketing pushed Nolan's name so hard, I recall multiple people thinking he directed it himself. MoS was coming off the back of both the Nolan trilogy which was immensely popular and Avengers which shot superhero movies into the stratosphere. So it's not really fair to use Returns as the only factor when talking about expectations either. Speaking of Avengers though, that's really the reason why expectations became so warped and it's common for people to think it flopped when at worst it may have slightly underperformed. Avengers took superhero movies to new box office heights. Combine that with the fact that Iron Man 3, the first post-Avengers MCU movie, broke a billion WW, people expected that kind of momentum to continue with MoS. That's completely unfair though, which is why the otherwise strong first film performance of MoS is framed so bizarrely.