"Good" self healing? More like "I will now heal to full in one button press and trivialize the existence of healer and damage intake".
Just because content is deemed casual doesn't mean we should further remove any degree of challenge or thought process in them. The further you diminish and automate it, the more you have to ask why are you even playing it in the first place.
And yes I do compare instakill buttons with those old self healing toolsets. They were insanely broken and were an upset to reasonable balance amongst the tanks in dungeons and any possible future horde type encounters. A single tank shouldn't just straight up be virtually invincible.
Self heal still exists and is more fairly rationed against content and other tank toolsets.