When it originally launched. The fact was that before the rework Mercy wasnt viable in higher ranks for a lot of reasons even before Ana came out and she was the only main healer and its because her ultimate was worse than the other 2 defensive ults.
It required failure to even activate and coming back from that to potentially die again is pretty lackluster, especially when the other 2 could keep you alive in the first place.
It limited Mercy since people not only needed to be dead in a 15 meter radius, they needed to be dead within the same 10 second interval which also required Mercy to stay alive.
In fact, every change that Resurrect got when it was her ultimate was a net buff, including invulnerability because despite being instant, Mercy would die often to do it, which still happens today and even more so with the cast time but its less of an issue since you arent bringing back a whole team to die again without their main healer.
When Valkyrie came out, it was good if they kept the limitation of one resurrect per 30 seconds with no way to reduce or refresh its cooldown.
The problem was the Valkyrie made it so upon activation, Resurrect was instantly refreshed and the cooldown was reduced to 10 seconds for the 20 second duration of Valkyrie. Essentially you could get 4 resurrects in 20 seconds by using rez, activating valkyrie, rezzing again, waiting 10 seconds and rezzing again and then another 10 seconds.
All that without having to worry about the biggest issues with mass rez since you could resurrect people when they died no matter how far apart they were or whether they were in the same 10 second interval.
They made changes so that instead of refreshing the cooldown or reducing it, Valkyrie just got 2 charges but that was still too strong.
Then they tried somwthing they shouldnt have since it wasnt the problem and added a cast time out of valkyrie but left the interation with valkyrie to make resurrect instant and have 2 charges intact.
The final change was what made her balanced because it removed the way resurrect interacted with Valkyrie.
They should have removed that interaction first and then tried a cast time but alas they did not and never will now so its a moot point.
Even during the penultimate change to Valkyrie, Mercy was statsically getting more resurrects per game than she ever was with mass rez which was due to the removal of limitations from the old resurrect and increasing the versatility for its use.
1 instant resurrect every 30 seconds is pretty balanced. Baptiste has immortality field which is a better version in many ways since it prevents a death in the first place which is objectively better, it has a lower cooldown, it has a near instant cast and can be thrown, its aoe and also applied to baptiste and thus has much more versatility as it can be used to save himself, and the most important part is that despite the drone being stationary, the drone has a smaller hitbox than Mercy and lacks a critical hitbox. MErcy is practically stationary for almost 2 seconds ayway and often enough she dies before getting the rez, dies after the rez, has the person she rezzed get killed again, or often enough both of the latter 2. Mainly this comes from trying to use it in the only time it really makes an impact and that is during a fight. Using it after a fight is already over means you didnt use it when it couldve changed the outcome of a fight.
So yeah, they’re fine with her now, but they said that repeatedly when she was being nerfed and said that recently as well only to then buff her healing anyway despite saying she was fine.