She may be considered “well designed” in a vacuum, but when you consider her relative power level against the other characters in the game its just simply not healthy to have an outlier like Tracer.
If Overwatch were filled with characters that had extremely high/infinite skill caps then you could make a valid argument that Tracer is good for the game… but a lot of the other characters that require good aim, and good positioning just aren’t allowed to have the same impact that Tracer has because they all have inherent weaknesses. Almost all of the weaknesses Tracer has due to her low health pool are vastly offset by her mobility and the sustain that recall grants her.
The heart of the issue is the Overwatch team undervalued mobility when they were creating the original 23 heroes and everything they’ve done to try and give players more counters to mobility has just ended up countering the less mobile heroes more than the flankers. At some point they’re going to have to admit their mistake try toning Tracer down just a little.