I’ve been watching this thread for a bit now so I’m just gonna go ahead and give my two cents.
At first, I didn’t have a problem with her rework but nowadays, I’ve realized that the rework hurt her more than help.
My biggest issue with it was that it completely changed Mercy’s identity.
“She is known to be the best single target healer” - Valk now introduces chain beams which kinda steps on Lucio’s shoes
“Mercy is known for resurrect, and this rework fixes hide and rez” - Now she has to hide to get rez off, and rez itself is a shadow of what it once was.
Plus back then, when she had Mass Rez, she was fun and engaging and balanced. You mainly saw Mercy from bronze to plat, and then Ana started to take over. You hardly ever saw 5-man rezzes in GM or T500 because it was too risky. Most rezzes were between 2 and 4 people.
As for the argument of Molten Core, I don’t have too much experience as Torb, but from what I have played of him, using his ult encourages a more aggressive playstyle. You have more of a reason to take his gun out, you can tank the damage for your turret while you hammer it to Level 3, and then you can charge the enemy. Valk, on the other hand, encourages a more passive playstyle. I have seen too many clips of Mercy using Valk and just goes to the skybox, and…that’s it. She might switch from heals to dmg boost depending on what the team needs, but what she does in Valk is the same as what she does normally. Just she now spreads her wings and moves faster. Molten Core makes Torbs be more aggressive, take out his gun, and makes him more of a tank. It’s easier to see value in Core than it is in Valk. Anyways, I am sure Torb mains can speak better about that than I can so I’ll leave it at that.
With Mass Rez, there was some strategy for it. Mercy’s sense of ult economy had to be on point. She had to have an almost spot-on feel for who on the enemy team has ults. Does Zarya have Grav? Does Soldier have Tac-Visor? And then she has to figure out if she should let her tanks fall first or rez and then patch them up, or if rezzing will even give them a chance to win or if it will just set them up for another team wipe.
And most of the time, the Mercy players don’t go afk and then press Q. They are healing the entire time until they can’t afford to (like if Soldier is using Visor since he could follow the beam to find the Mercy), and then when they get the chance, they swoop in for the rez. Even then, we have ults now that would counter a full Rez. Self Destruct is timed so it goes off the moment the rezzed can move. Minefield would counter Rez. Rip Tire counters it. So long as you don’t waste all your ults at once, Mass Rez could have its value completely nullified.
Last few points here: Another one of my complaints is the double standard here. We are allowed to completely change Mercy when she was balanced (even slightly UP for some people) but unfun to play against. Yet when Mercy mains complain that she is unfun to play as, that is an invalid point because she is balanced now. But she was balanced before as I mentioned above. She was only good in low ranks but was a niche pick in higher ranks.
Also, with supports, they have always kinda been treated differently. If Rein and Zarya are the meta tanks but the off tank feels more comfortable playing D.Va, the team can work around that. If the meta tanks are Winston/D.Va, but the main tank feels more comfortable playing Reinhardt, the team can work with that. But with supports, they have to play the meta supports. If the meta is Ana/Lucio, you have to play Ana/Lucio. If you play Mercy in this meta, you may as well be throwing. You hardly ever hear “Hey Winston, can we get a Rein” but hearing “Hey Mercy, we need an Ana right now can you switch” is not unheard of. The opposite happened before too where Anas were constantly told to switch to Mercy because that is what is “Meta”.
Which is the perfect segway to my last point which is not exclusive to supports or Mercy: People look at the meta to determine nerfs or buffs. One of the arguments I have seen against Mercy buffs is “She was meta for a year; therefore, she needs no buffs” or something along that vein, and pardon my French but honestly? That’s a stupid argument. The meta shouldn’t really determine nerfs or buffs. Zen and D.Va have both been meta for a pretty long time, but are they getting nerfed any time soon. Nope! The devs have said that Zen is in a good spot, and D.Va just got a buff with the shotgun changes. Hog has not been meta since S3 but did that stop them from bringing falloff to his alt-fire? Nope! So meta shouldn’t really be a factor. If they are a must-pick or they are not fun for either side, sure. We can take a look at them and try to find a change that would keep things fun and not disheartening for both sides. But just because they’ve “had their time in the sun” does that mean we shouldn’t buff them? That’s not a good enough reason to keep Mercy where she is.
Her winrate is continuing to drop, and after checking Overbuff (since that’s about the best we have in terms of stats), her winrate is now the lowest in the entire game, even lower than Bastion and Roadhog. And in GM, every hero has a 50+% winrate, except for Mercy. But Roadhog needs buffs because of his low winrate, but Mercy, who has a lower winrate, is balanced.
Okay, that’s enough ranting from me. For now, at least. This seems like a handful to read, to me at least, so here is a brief TL;DR: Mercy is a shadow of what she once was; Valk encourages a playstyle that is too passive; the rework goes against what Mercy was supposed to be; and her winrate is continuing to drop lower and lower.