Honestly, I believe that the sole reason Mercy was nearing 100% playrate was because of the mindgames that were behind having her on a team. Her kit has always been lacking on the utility side of the supporting spectrum. compared to Lucio she was lacking in overall utility, with her Ressurect obviously being the big things she had going. Zeny actually had more utility than Mercy but his HP pool simply made him unviable. Not the fact that he healed for less or that his ult was bad. No.

Add onto this that solo healer comps weren't that good (except for maybe KotH where teams sometimes ran solo Lucio) and you basically had to fit a Mercy and Lucio on your lineup.

Now comes the tricky thing. You don't want to risk not having a Mercy in your lineup when the enemy had one, simply because she essentially gave her team a numbers advantage. As a result of this mindgame, teams didn't want to risk being ''outnumbered'' so they ran Mercy, despite her lack of utility.

Fast forward to now, and her lack of utility, as well as the buffs to Zeny cause her and Zeny to swap roles. Most of us Mercy players are simply afraid that she will remain in this state with virtually no reason to fit her onto a team unless you are going to hevaily rely on her high risk medium reward Ressurect. A risk that can be negated by Zeny's 300hp/s heal during ult to prevent teamwipes Mercy is supposed to undo.

It's not that she got nerfed into the ground, it's that her weaknesses have finally taken their toll and unless she gets something new to play around with that offers more utility, she will remain in this state.