If you don't want healers to be a failing point for the party, then what DO you want to be the failing point? This is the question the devs have not answered in earnest.
If you don't want the healer to be the failure point, then tanks and DPS need to have enough sustain (provided they are performing mechanics correctly) to not die without the healer. That means unavoidable damage must be minimized - which trivializes the healer's role, and leads to the current complaint of "My DPS rotation is too simple/boring,* because if the DPS and Tanks have their own sustain then what else is the healer to do? DPS. And at that point, why bother enforcing a Healer in 4-man duties?
By trying to work around the ideology of "healer is not the party failure point," you trivialize and effectively remove the role of healer. If, then, for argument's sake we say "ok, since the healer isn't allowed to be a failure point and another DPS can help us clear faster, we don't even use healer," you need to have a failure point in mind and in place. And it needs to be non-trivial to avoid.