I didn't see the movie as saying Natasha had to die because she had been a bad guy or did bad things (or is that what the Russos said??) but because she happened to be better than Clint and so won their sacrifice game. Like, we never really saw Natasha do anything bad, we're just told about it, so her death looked more like tragic sacrifice of a hero than a necessary redemption.

...that sounds like I'm okay with Nat's death and I really am not, I am not a huge fan of heroic sacrifice anyway, and that her death get a minute of 'aww too bad' while Tony's gets an orgy of grief...even though Nat is the one who was holding them together for five years and most of them had barely even talked to Tony in that time, but Tony is more important to audiences so is more important to the characters.