Good Widowmakers dictate games. When you play against a person who just pops all your offense characters and supports without breaking a sweat, you're going to have a bad time. It essentially means you HAVE to kill that Widowmaker first, which is hard to do with 5 other people in front of her unless you have your own Widowmaker. Even with a counterpick of Winston to jump her, all it takes is a pocket Reaper and Winston can't do anything to stop the Widowmaker, and the Reaper can still contribute to defense and get back to the Widow to protect her super quickly, so you're back to being forced to counterpick Widowmaker with another Widowmaker.
And that's when a character is likely problematic. When the best counterpick to a character is the exact same character, there's an issue.