Karazhan was one of the best experiences i had as a healer in 5 mans since Cata.
Karazhan is a perfect example of how to make content challenging without pushing everyone's mistakes onto healer.
It was one of the most enjoyable experiences i've had as a healer in legion. Bosses had enough of steady damage to heep me on my toes without being too stressful, and i still felt impactful since i could remedy someone's minor mistake or two.
At the same time, if someone was failing hard they were going to get instantly killed or getting entire group killed instead of forcing me to struggle helplessly against overwhelming damage that was not intended to be healable, like in mythics+. Like a damage dealer standing in shit and saying "HEALER???" after he dies there. When someone fails in Kara it is obvious who it is.
For the first time in a long run, healing in 5man felt like fighting my own battle against boss mechanics while still being able to help others to some extent, instead of being a scapegoat paying for every single mistake made by your group and basically doing nothing when ppl were not making any mistakes.