I've seen, or rather experienced, both scenarios back in Abyssos.
Both DPS dying to basic raid-wide AoEs because they couldn't be bothered to press their mitigation buttons and dying to boss autos and bleed damage over the course of 5+ seconds despite full mitigation on the buster because the healers thought 1 oGCD was enough.
And I couldn't even blame them, it would've been enough for most of Shadowbringers and Asphodelos, which is pretty much all the savage healing they had experienced thus far. Anecdotal example, in E8S our Scholar didn't need to cast a single GCD shield outside of downtime where they had nothing better to do anyway.
I mean, it is true. I basically don't even think about what tank I get in dungeons when I heal because it simply doesn't matter. I go through the same healing routine I would use for Dark Knight even if I get a Warrior, sure they don't need the healing but it's not like I'm gonna use those resources on anything else.
That's not to say "who cares it's casual content" is the right response, instead we should ask for dungeons to not be so incredibly braindead that it doesn't make a difference whether you get the "immortal" Warrior or the "wet paper bag" Dark Knight, and then we can look at bringing Warrior's multi-target healing down to acceptable levels.
Because right now you could nerf Bloodwhetting into the ground for dungeons and it still wouldn't change anything.
