I think I can explain it. The person who suggested it has never played Mercy, doesn’t know how the character works, has no idea what she needs and doesn’t need, and had to say something anyway. They knew that dash reset is pretty critical for Genji and figured - how different could it really be for Mercy?
The change is so ridiculous. It will basically never have any effect in any game. It’s on par with giving Mercy 65 hps while her and her heal target are both in the spawn room, or giving Mercy a GA reset whenver a child by the name of Angela is born in Switzerland. The best that can be said for it is that it’s harmless.
Mercy didn’t need any changes, but if they wanted to try something out there were a few things they could have done that would have been nice to try. They could have shortened the switch time from staff to gun. They could have made Valkyrie not disconnect beams on activation. They could have requested a hybrid option for GA.
It’s not just this. It’s actually much more specific. You need a finishing blow, after using GA to engage (which you never do), you need to get it almost immediately after the GA in order to get any kind of cooldown reset on a 1.5 second cooldown, you need to almost immediately acquire a new team mate to target, and then you need to have whatever sliver of a second you salvaged off of GA’s cooldown to be meaningful. And all of this needs to happen in Valkyrie, where mobility isn’t even a problem.
Even if you go full, pistol only, battle Mercy, this change will very rarely result in a GA cooldown reset, and it will be much rarer than that for the reset to matter.