Summary edit after a few pages of the thread: I believe that what healing plays like varies too much depending on your group. In a great group the tank mitigates well and the DPS interrupt and avoid fire and you've got too little healing to do, but in a bad group the tank gets wrecked and the dps fail mechanics and there is too much for the healer to keep up with. Healing should be tweaked so that it is fun and challenging all of (or at least more of) the time, instead of only when you have JUST the right mix of group skill + ilvl + content difficulty. DPS aren't bored in an easy dungeon, they still get to blow stuff up. Tanks still get to be the center of attention whether it's mythic+10 or a random heroic while wearing 870 gear. But heals have nothing to do when content is easy or groups are good (or both), and too much to do when content is hard or groups are bad (or both).
Encounters, overall, could stand to have lower avoidable damage... and instead have more unavoidable damage, plus mechanics that penalize people for failing mechanics with things other than just raw damage. That way healing tends to be harder when content gets harder, regardless of your group, but without being entirely steady and predictable, and the incentive for the group/raid as a whole to follow mechanics remains, with the reprecussions for failures also being more immediate and apparent.
Original post: You're only ever 1 GCD from failure, it feels like.
Spam your fastest heals on the tank. Panic while you watch hp bars at 10% while you try to cast that ae heal that takes a nearly-endless 1.85 seconds to finish. Struggle against mechanics that force movement while also dealing tons of damage. Try to sneak in 4 seconds of a mage biscuit between pulls since there's no such thing as mana conservation in dungeons and you know you'll need a bunch of mana for the next fight that the tank and dps have already started 65 yards ahead of you since they have no direct incentive to slow down as long as youre willing to bust your ass to keep them alive.
I feel like Dagny Taggart and Hank Reardon in every mythic (and especially mythic+) I run, burning my candle at both ends to let the other 4 people in the group play exactly the way they want to and not a bit differently, secure in the knowledge that they can probably get away with blaming the healer if anyone dies even if it was their tunnelvision on meters and a timer that truly caused the deaths.
Why does it have to be like this? What ever happened to those times Blizzard said they were going to boost hp pools relative to damage coming in so that a player PVPing can't die in a stun lock to another single player, or a tank can't be dropped in 3 seconds from full? To them saying they didn't want content to be just a mad spam of the most powerful spells? To the days when tanks had aggro to worry about so they couldn't just facepull 3 trash packs at once to be AEed down? To the days when DPS, too, could oom or pull threat if they weren't at least a little careful?
Or am I just bad and/or playing with bads?
Why can't we have more to think about but less to frantically mash our way through? Why can't a DPS failing a mechanic stick that dps with a big damage debuff and some damage instead of just a ridiculous amount of damage for the healer to deal with? Etc.