Nerfing Mercy because she is popular is not a good strategy.
It is mathematically incorrect to patch for political reasons and not for actual fairness, but there is more to the topic:
Lately the balance patches have damaged the game’s reputation and the latest hero releases didn’t help much either.
Mercy is not overpowered, all other healers are clearly underpowered.
They all do “something” but certainly don’t heal properly.
It would be fine if there were “some” supports that only do part-time healing, but Mercy is the only support who’s focusing on healing.
Ana and Moira have strong healing power, but are still no alternative to Mercy.
Ana has no aim, you often don’t hit the target you want to hit, simply because she’s projectile based.
If she was at least hit scan as Widow is, then she’d be more viable, but she’s not.
Furthermore Ana has hitbox problems: When the hitbox of a large hero encompasses her or at least is where her projectiles or her grenade are emitted from, then she sometimes hits targets behind her.
Furthermore Ana’s heals can be blocked, Mercy’s can’t which already makes her less fun than Mercy because you feel useless when someone needs heal and you can’t provide it, because there is a 5hp shield bubble in the way, or too many heroes between you and the target.
Uncertainty at healing is a clear no-go for any healing class in any game.
Moira is forced to be a part-time healer, putting herself on the front-line at risk, because she needs to charge up her healing resource.
To wrap it up quickly: she can’t do what she wants, when she wants.
And to top it off one heal is ranged but has a hefty cool-down, the other is purely melee and cone projectile based. Highly unreliable.
Zenyatta has a HoT that runs out when line-of-sight is broken, which is already a downside, since the only thing that would make him viable - healing flankers - doesn’t work because flankers usually aren’t where Zenyatta would go.
Furthermore he really has been turned into a damage dealer and therefore can’t be given a strong heal. He is not really a healer.
Now look at Mercy:
She doesn’t deal any significant damage, she loses every 1 on 1 battle, unless there is a skill gap which is to be removed from the equation, since it has no meaning.
The only 2 things she can do is heal someone with a reliable healing beam or buff their DPS a little bit.
Now the damage buff has already been nerfed and doesn’t make up for the DPS of a Zenyatta, therefore it is only reasonable that her character forcus should be at healing, if you see the others as constants.
But now we also realize she is the only healer you can pick, simply because she is reliable; and of course that might be the reasoning behind the nerf; but this just makes the game worse.
The other healers aren’t fun to heal with. Or at least aren’t “as much” fun.
Simply because they’re bad at it, they never save a life, except for Ana when she occasionally actually hits her target and that’s a big question-mark, since the enemy team has control over her healing power through shields and body blocking.
So nerfing mercy doesn’t make the game better, it makes the game worse.
Even if you would counter me with “it is mathematically actually correct”, which is the only thing I can’t tell because I don’t see your equations, it is still a bad idea to “reduce” the capabilities of a hero to balance them.
It’s not fun to feel useless when a team mate dies in front of you despite you trying everything to heal them.
It’s okay if you have to choose whom to save and maybe manage to save more than one by managing your powers wisely, but it is not fun if healers are just damage dealers with a little twist. You can do that with one or two heroes for diversity, but not make them all the same.
I’d highly recommend to increase the healing power and reliability of a few heroes instead.
