Torb’s meter grows passively and by him doing an action (gathering scrap). Same as every hero’s ult.
But the asks for a Rez-meter all mention no passive gains. So what would be her action? What would fill the “gas tank”?
Healing?
That fills her ult. And setting it any lower than her ult requirements is a bad look. “Oh, I need X amount of healing to not be able to do enough healing to counter any ults, but 1/3 X (or 1/2, or whatever) will allow me to bring someone back from the dead?” Rez is more powerful than her ult. So, we can’t make her meter lower than her ult, and we can’t use healing.
Damage-boosting?
Sure, performance-based SR has been removed for Diamond and above. But for players that are lower, there’d be no way for them to get out of “elo hell” by being the best Mercy. Because they’d be at the mercy (no pun intended) of the aiming skills of their cohorts. And players in bronze (speaking from experience here on both parts) pretty much can’t hit the barn-side of a broad. (I know, it’s supposed to be broad-side of a barn, just sounds funnier my way.) So using damage-boost doesn’t show how good of a Mercy you are, it shows the aiming skill of your team-mates.
How about her own pistol damage? Well, that now gets into encroaching on Moira’s shtick of doing damage to “heal”. And Mercy is supposed to be a healer not a DPS. Her pistol isn’t supposed to be her primary weapon (that’s why it’s on 2 and her staff is on 1). So that’s out.
And that now leaves nothing with which to charge up a rez meter.
The best way to make her rez earnable again is to lock it behind her ultimate.
And here’s my idea that I shared in EeveeA’s post:
I’ve been a staunch hash-tag RevertMercy poster, but I would be happy if this rework variant were put into the game. It gives her back the possibility of swinging a fight towards her team’s favor. But it’s not oppressive like the original rework, yet keeps the more mobile aspects of it that many people have found enjoyable.