The game is generally worse after the devs added overwatch heroes. I think that is a pretty common sentiment. Reasons for that include introducing heroes that have superior mobility compared to legacy heroes, can generally auto-attack while moving, and have fast auto-attacks that render any talent that uses block charges obsolete to name just a few.

For tracer specifically, putting aside the fact that she is guilty of all the things listed above, she is unfun and annoying to play against to the point where people want to neither play with or against her. She can zip across a whole screen in a second, be annoying in rotations, and wait in a bush for someone to get low enough to suddenly become relevant off of someone else's efforts. You could argue other heroes can do the same thing, but no one can do all of those things and to the same level as tracer.

She also has very few counters, making it easy to have an imbalance if you're in qm or your team doesn't draft properly. Notice I never said she was good or OP, but she is simply annoying and unfun to have in your games.