Sick burns. And yeah, after IM2, Black Widow was kind of... there.
Could they have done more with Widow? Holy poo yes. Did they? No. Ever. She's the same in IM2 as she is in Endgame.
The closest thing we got to actual black widow development was when Barnes was choking her to death and she said "You don't recognize me? Really?"
When Marvel decided to have the winter soldier kill Howard and Maria Stark, I understand they had Black Widow involved. I don't know how, I didn't read those issues.
But holy poo.
Plus, the comic black widow, as well as Fury, have the Infinity formula, which slows aging significantly.
I remember wondering if Wolverine took Fury's eye in WWII, but no, Natasha is a 1980's Soviet spy/hooker, and Fury is... I think a marine? I did not enjoy Captain Marvel. And yeah, Captain Marvel made it canon that Fury lost his eye to an bottom alien cat.