The Aggressive Renewal channeled damage ability in Inquisitor fills my power bar up about 75% of the way if it is allowed to channel for the full time. That being available every 30sec along with the power reduction ability in inquisitor will keep you from being power hungry. The Harsh Discipline channeled damage ability is much less useful in healing, but it does help a bit. Being on a 1min cooldown also makes it less useful. I put them both in a macro with shards of light (Sentinel) or distorted shadows (Cabalist) as the fallthrough channeled ability depending on the build. The armor buff in inquisitor also helps keep you from being so squishy with a nice endurance and armor factor buff.

But, I agree, for boss battles, the passive healing available in a cleric build isn't enough. However, their access to effective instant active heals more than make up for that, depending on the numbers in your team. I have a much easier time with rift bonus bosses in my trio of clerics than I had when leveling up my trio of rogues. But I'd assume that scaling up to a full group, the passive healing capability of the bards would work good enough.