I don't see how. It's the same thing, it'd just take more casts. As it stands now, I can spend over half my time not healing, easily. People pushing it to the limit can wind up barely doing any healing at all. That doesn't strike you as a problem on a role called "healer"?
There's plenty of room to make healers devote more casts to healing without making healing impossibly difficult. Those casts are coming out of DPS and/or stand-around-doing-nothing time. They also reduce the need for one shot mechanics by making killing people with periodic damage and running healers OOM actually feasible, which simply doesn't happen in most content right now.