I understand that Mass Rez is never coming back, and the devs are merely going to iterate on current Mercy, but there are still quite a few things I liked about Rez.
At the time of Mass Rez, we had nice interactions between the healers. We had a main healer with an offensive ult (Ana with Nano Boost) and a main healer with a defensive ult (Mercy with Mass Rez). On the flip side, we had an off healer with a defensive ult (Zen with Trans) and an off healer with an offensive ult (Sound Barrier). From my experience, Lucios primarily used that to start a push.
Also, Mercy having a defensive ult is completely in character for her, given that she is a doctor. She has the namesake Mercy because of her unwillingness to turn to violence. So Mass Rez was in character for her since she has brought people back in the past (Genji) and it fits her role as a doctor since her job is to save lives.
Another thing that I liked about Mass Rez was that while we had plenty of DPS and Tank ults who could wipe the team by pressing Q (Self Destruct, Grav with followup, Shatter with followup, Blade, Blossom, Barrage, Visor, Noon, etc.), with Mass Rez we had an ult that could bring those people back by pressing Q. So you would essentially counter someone’s Q press with your own Q press.
One of the complaints I have about how people view Mass Rez is the whole hiding bit.
When Mercy is not in the fight and is waiting for the right time to use Rez, she is “hiding”. Yet when Reaper stays out of the fight to wait for the right Blossom, or McCree is waiting for the right Noon, they are “taking cover”. How are these DPS players staying out of the fight to wait to use their ult any different than Mercy doing the exact same thing?
Also, I have seen a few people say that saving your ults to wipe again after Rez happens isn’t counterplay, but it is. It’s rendering the value of Rez to be practically useless. She swooped in to bring her team back, only for them to be wiped again. She essentially used Rez for no reason because her team just died again. I am pretty sure that rendering her ult useless is the definition of a counter. It also encouraged players to keep track of the ult economy. You don’t just go bursting in like the Kool-Aid Man and use up all of your ults. If you have a good feel for the ult economy and you think Mercy has rez, then you stagger your ults. Only use one or two of them to wipe the team, try to bait out Rez, and when that comes, pull out your other ult. Mercy uses her sense of ult economy to know when a big push is coming. Mass Rez encouraged others to have a similar sense of ult economy to know when to save ults.
Last thing I’ll say here: I honestly don’t pay attention to the people that are asking to revert Mercy’s rework because I know it’s not going to happen, but much of the complaints I have seen about New Mercy (and one that I have myself) is that she does not feel engaging. For the most part, the heroes in this game, while relying on teamplay for the most part (tanks and supports especially), they still have some part of their kit that can be performed on their own. Zen and Lucio can defend themselves without having to completely rely on their team. If Ana was dove on, she could use sleep dart to render the flanker idle for a few seconds. So she had that ability that could be used without relying on her team. And there are plenty other examples from tanks and DPS that I can pull as well. Mercy right now, however, does not have any part of her kit that cannot be performed without her team. Everything she does, from GA to Valk, relies on her team. And Valk right now feels more like a spectator mode than anything. When other supports use their ult, something about them changes. They do more healing, they enhance someone’s performance, something about them changes. With Mercy, how you play her during Valk and how you normally play her is the exact same. The only noticeable change at this point is the chain beams. Everything else is either minor or otherwise unnoticeable. So since they are not reverting her, I think that any change they can make to make Mercy more engaging would be appreciated by Mercy mains or just people that pick Mercy now and then.