Friendly Reminder: All Healers are not equal and some are countered by heroes easier than others.
Obviously there's something to be said for "protect your backline" in terms of off-tanks peeling for healers or DPS specifically looking out for certain attackers that target the backline.
That being said, know that not all healers are created equal in terms of "I'm a healer". Just as DPS and Tanks can be hard countered by certain characters, there's absolutely certain characters that counter healers. Knowing when you're being countered and making a switch is important instead of blaming your teammates for you dying every 20 seconds. Some general notes:
Zen and Ana are the most diveable heroes in the game. They are by far the least mobile of the healers which makes them prime targets for flanking heroes. Doomfist can easily 1-combo a Zen low-difficulty, Dive Tanks can make life a nightmare for them both (since they're ranged healers and will be away from the teamfights often), and are prime targets because of this. If you find yourself dying often to flanking heroes, don't just yell at your DPS to go McCree and babysit you or demand your Zarya constantly look behind her to throw a bubble your way. There's a multitude of other healers that are not only more mobile (Lucio, Mercy, Moira) but there are other healers that have fantastic defensive capabilities against those attackers (Brigitte, Baptiste).
Mercy does a LOT of healing. It's not all impact healing. I have a hard time getting this point across to a friend who is a Mercy 1-trick. I constantly hear "I keep losing but I have 30-40% of damage healed every game! I always have gold healing!" What I don't think you understand is that hearing a healer say "I have x-amount of healing" is the equivalent of a DPS being hard countered and saying "I have Gold Damage". It's an irrelevant stat in the scheme of how the teamfights actually work. And although yes, you may be cleaning up every bit of spam damage and keeping people to max, there's a certain type of healing that is more important than others against certain heroes. Whether or not you're a solo-target healer (Zen and Mercy can only heal 1 person at a time), Area healer (Moira, Lucio, Baptiste), or burst healer (Ana, Brigitte). All of them provide healing in different ways that require changing based upon what kind of damage your team is receiving.
Know when you need a specific kind of ultimate or cooldown. Not all healer ultimates or abilities are equal. Transcendence and Sound Barrier are enormous defensive ultimates that have tremendous upside. Nano and Amp Matrix are offensively-geared ultimates and may not be what your team needs in order to win teamfights despite the fact you may be healing "a lot". Similarly, there are times when you desperately need anti-nade to punish an aggressive set of tanks, or a discord to burst down a target that is becoming a massive headache. Simply looking at the healing output you're doing is not an indefensible excuse when people ask you to switch or request something else.
Healers are as much as part of the game of "chess" when it comes to comps and synergies as any Tank or DPS you pick. Simply picking one does not absolve you of having to make constructive switchesto help the team win and simply having a healing medal is as worthless as a damage medal.
Source: Am Zen main.153 Read the full article on Reddit