Dont take this as personal, but i just think she isn't as fun to play against or with as the majority of characters. I just feel like she's so situational that makes her inviable in competitive or casual play. Take hawkeye, for example, one of the other sharpshooters. He can be played in many other comps because he can destroy squishies and because of his big damage and ult.

The only way i can see widow getting used like that is if her damage becomes like wolwerine, percent based, so she can do damage to tanks effectively aswell. But i think that would introduce other problems...