I know these universes exist independently - I’m talking about butterfly effect within each individual universe.

And I’m not just talking about MCU, I’m talking about any parallel universe concept, whether in fiction or real life theory. In two independent parallel universes, it doesn’t make sense for them to be mostly like each other but slightly different. Because the moment on difference happens within the history of one of those universes, the rest of the future should be completely different in that universe from the other.

Let’s take our universe, imagine there’s a parallel universe exactly the same, and go back in the timeline. What if JFK didn’t get assassinated? Then compare 2021 in that universe to ours, and things are completely different. To the point that I likely don’t even exist - because if our timeline of US presidents is different then all kinds of other decisions don’t get made, certain people don’t meet. Maybe my mom and dad never get married in that universe because the flow of the Vietnam War is completely different so they aren’t in college together, etc.

But as a fictional device writers tend to handle parallel universes as if a huge change only has impact in a vacuum. For example Captain Carter ends up coming back 70 years later and is in the exact same situations as Steve was when he came out of the ice 70 years later, with SHIELD exactly the same, down to Black Widow doing the EXACT same mission with Peggy that she was doing with Steve in the main MCU Universe? Even though I’m this one there was no Peggy Cater during those 70 years to start SHIELD?

>These universes exist independently of each other. Unless
>it's a multiversal event in scale, something happening in one
>universe, does not effect the other.