Devs, do not ask GM/TOP500 Mercy mains how balance her because, nobody will tell you how NERF-EFFECTIVELY their true-love character. No matter how professional do you think they are. Just look this forum how the people defend their mains suffering a total DEMONIC-FANBOYISM-POSSESION lol.
Ask your internal Winston mains, Genji mains, Tracer mains and Dva mains the "Counter of Mercy" how you can make her less effective. People devote their characters entirely to kill and counter support characters can tell you EXACTLY what she need in a more objective way.
As a DIE-HARD winston main with nearly of 500 + hours between all my accounts and my main account on GM.
Stop destroy Mercy in that way, these nerfs are not effective you are only making her EXTREMELY boring.
Mercy-changes: Give her instant-REZ during valk, during Valk she can mix power/healing beam, keep her at 60 Healing per second.
Mercy-nerf: The only Nerf she need is one or two EXTRA second on guardian-angel, this will ALLOW her counters can kill mercy effectively making her switch like most of the other heros. This ability should not reset under any ability-ultimate or increase speed-range.
In the present a good Mercy can escape of her counters cuz she can nearly “SPAM” guardian-angel, having this ability on a 3 seconds cooldown will make her a lot more vulnerable.
Test with 3 seconds GA if the pickrate dont go down in 30 days then add 4 seconds GA.