You are entitled to your opinion, and I respect it. I humbly disagree however. Because with the amount of counter-play that exists at this point, I don’t think an escape option would be all that overbearing, and especially so with things like area denial ults and more CC in this game being a thing. It’s certainly way better than Mercy having the res, ulting, being killed before the ult, and then having it again, ready to try again later isn’t it?
In terms of Valk and Mass res, I dunno about that. I think it’s certainly possible to have both. If the devs were able to figure out how to keep rez and valk in her kit currently, I’m confident that they can do the same if the abilities were switched. We will never know however if this will actually be too powerful or not until it’s actually tested out right? I would say then to atleast give it a chance. At this point, since Mercy is already one of the weakest offensive healers in the game, there isn’t much to lose with said risk. But that’s just my take on it, and you are free to disagree. 
~Sincerely Yours xoxo,
a Lover of True, Fair, and Fun Balance.
xavvypls 