It was harsh? Sorry about that, I was just commenting.
As for clarification, let's use the Winter Soldier example like you did. Witer Soldier did a heel face turn, but you forget that was not his first appearance, as it was revealed that he was actually Bucky Barnes, Cap's friend, who audiences had known and had much sympathy for the way he defended Cap and died in a mission. Then it was discovered that he was brainwashed giving him much more sympathy.
TL; DR, this was not his first appearance, he had been established before as a sympathetic character in Captain America: The First Avenger.
With Black Widow, what you are doing here is introducing her as a Free Agent hired by SHIELD, she has no allegiance to the organization save for the money they give her, and you have already mentioned plans of adding a Post-Credit scene where she is seen being hired by another figure in the shadows, even implying that all her actions were done in order to get "a seat in the table" as it were. Natasha does not come as a hero at all in this movie. I would even hazard to say that she is closer to her Ultimate's version.
Isaid it before, this is the first time that regular movie goers will see Black Widow, and their first impression will stick. And considering that Favreau will not have this Black Widow in his movie, Vaughn has his own plans for Power Man, and Johnston's idea for Captai America does not include Black Widow, then there will be at least a 2 year gap if she somehow manages to appear in Avengers. more than enough time for that impression to solidify.
Anyways, I have to update for my other quest. If any of you have any questions you can alwasy ask.