How many actually do?
Valk Flight is a hit with a lot of people but, it’s a miss with a fair number.
Single Target res as far as I’m aware isn’t actually that popular.
Chain beams is also of mixed popularity last I knew.
Valk’s currently on the long side ult wise and most Mercy comments/poll responses I’ve seen either want a big bang or a medium length ult.
I doubt the current Mercy is the ideal Mercy for even 10% of people that play the character. That doesn’t mean that everyone wants a revert tho.
You also don’t necessarily have to obliterate the current Mercy to get a different Mercy.
It’s entirely possible for Blizzard to add a new hero with a near identical base kit that has a different ult/other abilities.
Some of us did suggest this method for implementing Valk back when the rework was on the PTR:
Ex: (Some grammar/spelling errors)
Personally, I think the PTR Mercy might work better as a new Hero rather than just replacing Mercy as lots of people like each of the heros and dislike the other. If either PTR Mercy or Mercy is too annoying to a segment of the population they could be banned from their matches to allow for maximized enjoyment as Casuals might dislike the PTR Mercy and Competitive players seem to generally dislike the current Mercy.
TLDR: I don’t think the new Mercy is balanced. I don’t enjoy playing her much. I don’t enjoy playing against her. She is fun to watch. As lots of people do like her it might be better to make her into an additional healer instead of just replacing Mercy with her.
It wouldn’t be cheap but, they are the ones that made the design that ultimately whiffed on designing something that could be balanced while also managing to line up with what most of the existing player base for the character wanted.
They did something similar with both Sym and Torb where they whiffed on part of the initial audience but due to the characters low popularity they ended up in roughly the same spot via picking up a few more players that previously disliked the character.
Not sure if it’s the same for Baja but, when he hurt himself he was more of a mid range hero due to the self damage. The change made it so the character was frequently played closer.