I actually addressed this a few days ago for someone else who didn’t understand how balance can effect fun without changing the specific mechanics, though that thread has since been deleted.
We’ll start with Mercy as an example, and I’ll move on to other examples that I’m also familiar with.
At first glance, the change doesn’t seem like it should effect how much fun a player has. The character still plays the same mechanically, still fills the same role, the numbers are just different now.
However there’s a couple reasons why this is false. The first specifically applied to Mercy. With less healing means you will be less likely to save a team mate actively being attacked and more time spent topping people off. This means less time to safely heal team mates and then swap to damage boost, pistol, or even go to rez without risking someone else’s death. This specifically changes how Mercy players play without changing the mechanics.
And that’s not necessarily a bad thing on its own. But there’s another factor what makes a character enjoyable, whether it be overwatch, a moba, fps, rpg, or some other game.
And that is the character’s effectiveness. Now I hear you, you’re probably thinking “how good they are should not effect how someone enjoys a character. They either like them because they like them or they want to be OP.”
And for some (very few) people, this is true. But I haven’t found that to be the case with the vast majority of players. Instead, I have noticed the opposite to be true. People do genuinely love a character for either their themes or how they play.
But part of appreciating that means also being effective. No one wants to feel useless, regardless of whether you love a character or not. If a character is hit too hard, and they are too weak to effectively do their job, that effects the fun players will have. If other characters are able to perform the same role much more efficiently, you’re going to have unhappy players on your hands.
I’ll use D&D as an example as I love it and I’m familiar with it. One of the secrets a lot of DMs use but don’t tell the players is they want you to feel powerful. Feeling powerful feels good. This is why often players can be rewarded with magic items that enhance their strengths even further.
D&D 5th edition had a similar with a subclass for the ranger, the Beast Master. It is a super cool theme where you get a trusted animal companion. You can fight side by side. Hacking and slashing, tooth and claw! Or you can play a more hound master style character and shoot from afar while your trusted beast goes in for the kill!
Except… the subclass sucks. Hard. It’s so bad, you can actually get an animal companion as any class and the rulebook has a section for giving levels and xp to such companions. Literally any other class combination can do what the beast master does, but better.
Even if a player might like the mechanics that come with being a ranger, it feels absolutely awful when youare the bottom of the barrel because you cannot effectively do your job and others outshine you.
Back to Mercy specifically, I understand she needs to be balanced. I held this opinion before the nerf and I hold it now. Her healing was fine. It was good. She’s the classic doctor, she should have good healing.
Her rez is her issue. I don’t think hammering at her kit until she’s no longer busted to just keep the rez is worth it.