50 healing per second is too low. It’s not about the Mercy player’s skill, it’s about how much damage Mercy’s teammates take. No matter how skilled Mercy is, if her teammates average more than 50 damage taken per second, she falls behind, and there is absolutely nothing the Mercy player can do to come out on top of that situation. She doesn’t have the tools to deal with it, while every other support has some form of effective burst heal.
Resurrect is powerful, but like Mercy’s hard capped healing output it does not become more effective with Mercy’s mechanical skill. It even takes skill expression away from the player by restricting her movement. There’s some thought involved in timing, but in the end Mercy is at the mercy of the other players in the game to get that Resurrect off. It’s up to her friendly tanks to protect her if the enemy has any idea she’s there.
From a team perspective, Mercy is viable. She’s not a throw pick. A great Mercy makes a good team great. However, she’s completely incapable of carrying. A great Mercy in a mediocre team still makes for a mediocre team. Every other healer has the tools they need to carry a bad team over the finish line, but not Mercy. The other healers can erase teammate mistakes, but not Mercy. Not since the cast time was added to Resurrect, which prevents Mercy from using it on players who died out of position.
Mercy is overall balanced and viable, but she lacks individual impact and personal control over the outcome of the game. That is why you keep seeing and will continue to see posts complaining that Mercy feels weak, because she IS weak from the individual perspective. It’s a problem that Mercy didn’t have with mass resurrect as an ultimate because she was rewarded for being the last one alive. In that situation, Mercy could carry games, even when she was considered not viable at high rank. Now, she is helpless in that situation.
She needs a rework. She needs more individual impact and carry potential. Increasing her healing back to 60 would help without breaking anything considering her stats vs other healers, but even that would just be a band-aid fix for a missing leg.