Maybe I'm missing something? Hehe.
And, I would argue that the "Cinematic Universe idea" was proven to work long before The Avengers was released, it was a conclusion to something already known to be a success. The hype for the ending of Iron Man with Nick Fury showed that the audience were onboard.
And, saying that The Avengers "kickstarted" a universe doesn't really ring true to me, it was the 6th (?) movie in that universe.
Avengers was the culmination of a build up, but the magnitude at which the film exploded compared to the previous entries is what made it such a big deal.
It was the first film to open to more than $200m in a weekend. It didn't just barely beat the old record that Harry Potter 8 set, it crushed it like a bug. Then to have a $100m second weekend? That shit was nuts.
Hell, Avengers could have never released outside of the US and been less than $1m from being the highest grossing MCU film worldwide to that point. It was only the third movie to go over $1.5b worldwide as well at that point. It was a major deal just how successful that film was.
If it had just been a marginal increase over the previous entries, it would have been a success. But it was an absolute monster that took almost everyone by surprise. Following the box office tracking that weekend was very interesting, because the numbers kept climbing and climbing and people didn't know what they hell to think or predict anymore. NOT A RECORD!