The problem with your interpretations of bare minimum here is that it intrinsically relies
incredibly heavily on healers. You can clear absolutely any content in the game if your healers keep everyone alive all the time, literally the only thing that could ever kill you is a hard enrage which would be hard to hit on most fights if every player is always alive.
Also to take it one step further this could mean people ignoring mechanics and avoidable AoE because, as we established, it's the healer's job to keep them standing.
The problem here is in the astronomical difference in difficulty that can be presented by some players or groups. We have all had some sprout run off with the stack marker or a tank who plays disco boss and cleves the group. Keeping everyone alive in these situations is impossible sometimes
and that's okay.
In it's fully simplified version the bare minimum for every player is killing the enemies while staying alive. This means tanks become responsible for aiming cleves away, DPS need to dodge AoE and healers need to do damage where appropriate. We all help each other with a variety of support abilities that are not relavent to our primary roles because it just doesn't make sense not to. As a healer's primary role
is support the way we help tanks and DPS is by helping them kill the thing. That is our 'extra', our 'proper positioning' or 'Refresh/Tactician' or even just 'moving out of the bad'. Our utility is our damage, it may not be baked into our basic responsibility like tanks or DPS but it is certainly something that should be expected of us within reason.