Evans plays Captain America as humble, even reluctant. That has never been my impression of the comic book version. He’s always been depicted as a strong, confident leader type. To my mind, this completely contradicts his origins. It’s easier to see how the movies nail it, because they’ve been developed over a shorter period of time and they had to think about these things. Captain America when he originally debuted was a gung ho soldier, but by the time he was brought back in the '60s was turned into just another superhero, an Avenger who was naturally assumed to be a leader because, well, he had “captain” in his name and he’d actually been a soldier.
But going back to Evans, I can’t really fathom why he wouldn’t have agreed to do the one mission (take out Loki) and then just decide to walk away. There’s no upside. But I guess that’s why he became associated with SHIELD, and why Winter Soldier made so much sense, because it did take into account why and how he would’ve stayed in the business. But it also was a natural separation point. He almost seems to have a Michael Corleone complex.