Originally Posted by The Endless
It's not a fan theory. It is what it is. The solo movies are the same as the solo comics. Do you complain that Stark doesn't help Cap out in every Captain America comic? Or vise versa?
No you don't because whilst they are in a shared universe you suspend your disbelief and understand they are individual stories.
Perhaps that's why you do it. For me, there's two reasons. I hold comic books to a much lower standard of realism because they are drawings, and because they are aimed at people who started reading as kids, but are no longer kids, people who still have a certain amount of childlike indifference to reality and, as you put it, suspension of disbelief.
The second reason is that the comic book characters have a different culture. For them, saving the world is just Tuesday. In the 616 universe, it is mathematically impossible for Captain America to be there every time the world is threatened, or every time some mad scientist is doing something unthinkable. It just happens too too often. So much so that he naturally trusts other people to do incredible world saving on their own. What sense does it make to run to help Iron Man when Iron Man has single handedly saved the universe 5 times?
Now the films, they don't have that culture, either in or outside of the story, so I point out when things don't make sense, because the solo films are not really like the solo comics, they simply draw inspiration from them.