I’m not sure where this is coming from.
The support class is not balanced, especially not at high ranks. Statistics (both win rates and pick rates) show that Mercy is a really bad pick in diamond and a throw pick in master and GM. She’s bad to mediocre in gold and plat. She’s not in a good or viable spot. Not even close. When you have a character that’s as far from the tier win rate averages as Mercy is, it’s a clear indication that they need a change.
Furthermore, the rest of the support class balance isn’t as great as you make it out to be. It’s better than it was two months ago but worse than it was four months ago. For instance, in high ranks Ana is just as much a must pick as Mercy ever was.
I wrote a post detailing this