Viable: Capable of working.
Optimal: Working in the best way.
Confusing the two is bad. Using Smite is meant to stay viable. The problem Blizzard was facing is that the talent points were too weak to be considered viable due to the buff to Heal. Smite's scaling was improved so as to not punish people who liked using the talents.
Blizzard has never stated that they want Smite healing to be how Discipline heals. Only that they want the option there to satisfy the cries for a Smite spec. They did not want Smite to be competitive DPS, so they designed a way to make it into a heal through Atonement. Nothing more, nothing less. It is what they have repeatedly called a 'fun' or 'optional' setup. There is a very long way to go before it is an optimal setup.