What I've seen in group testing so far is that as long as the DPS uses a Finisher at some point, there isn't much need for a Power Healing Controller. At max stack, using a Finisher should replenish almost your entire power bar. If a DPS doesn't use a Finisher, no amount of Power Healing is going to help a DPS that is spamming 200 and 300 base power cost powers. Without a Finisher and with a Power Healing Controller assisting, an Electric player used up all their power at ~11 seconds. Using a Finisher roughly every 10 seconds, they could sustain their rotation indefinitely. Having a Buff Controller along was more than sufficient if the DPS used a Finisher.