Shakes

I disagree that this is the case in WotLK. With the buffs to healing wave (25% extra +healing, 30% cast reduction after chain heal and 60% healing after crit) it's the volume Shaman heal.

Chain heal scaling factors:

5/7 base
* 1.75 for jumps
* 1.1 for ancestral healing
* 1.2 for improved chain heal

overall = 1.65 healing per +heal

Healing wave scaling factors:

6/7 base
* 1.1 for ancestral healing
* 1.25 for Tidal Waves
* 1.18 for Healing Way

overall = 1.39 healing per +heal

Each point of healing gets an extra 0.5 multiplier when it crits for chain heal, but a 1.4 multiplier with healing wave due to the 60% ancestral awakening proc. So at some point of crit, healing wave scales better than chain heal:

1.65 * (1 + .5x) = 1.39 * (1 + 1.4x)

x ~= .223

22.3% crit for healing wave to start scaling better than chain heal. I currently, with 0 crit from gear, get about 10% crit just from int, plus with 9% crit from talents, I think this point will be trivial to pass.

So healing wave will scale better than chain heal. It will also cast 30% faster for the next two heals after using chain heal. To me it seems clear that chain heal will simply be something you cast to make your next two healing waves fast, not for the throughput of the heal itself.