You're preaching to the choir.
The important difference is that failing a mechanic is widely seen as "bad play", and is thus generally discouraged. Which means that in the case where a group is having trouble with content, one of the possible ways to improve is to not fail mechanics, which will lead to less incoming damage. But if that "incoming damage" is coming from a part of a player's optimized rotation, that's not seen as "bad play". And thus when the group is trying to get past a roadblock, it becomes more ambiguous whether or not a specific behavior should change, and thus the table has been set for conflict.
In my opinion, one of the reasons that Final Fantasy 14's community tends to be so great and overall experiences with other players tend to be so pleasant is because relative to many other MMO's, the game's mechanics are crafted and curated to mitigate the potential conflict. A class ability where I lose some life but gain a buff is packed with potential for this exact kind of conflict, the kind that is easily avoidable by simply not having this mechanic.
Which is why I don't think that adding the results of "bad play" to the formula for "optimal play" is a good idea: it's not a significant enough change to be an actual solution to the pervasive issue of healers being bored, but it is enough to cause problems and conflict for less skilled players and groups with different ideologies. No thank you.
