Was this intended originally by Whedon? Probably not. But boy does it fit nicely regardless.
That's my whole point, though, it wasn't intended. Cap is the way he is because of different visions for what the character is. You can try and piece together some reasoning for why they're different and you could even find a pretty good in-universe explication.
At the end of the day, though, those reasons are to do with conflicting views on the character by forces outside of the story. Even in AoU Cap didn't do half the crazy shit he was able to do in WS because Whedon was directing him. In CW he's able to do what he did in WS because the Russos are directing again.