As others have pointed out, we nerfed all of the medium heals.

Very early in beta, some healers were freaking out about running out of mana. To counter this, we made the medium heals really cost effective. We probably overdid it, because more recently, healers were able to handle almost everything with just that one heal. We want it to be part of your package, not your whole package.

We gave Replenishment to Restoration because we took it away from Survival hunters. It didn't make a lot of sense for a non-mana class to offer mana. We want to make sure Replenishment is easily available, though to be fair it is about half as effective as it was in Lich King.

Keep in mind that we're not super concerned with healer mana efficiency when not in a group. Fights are pretty short when you're solo and there are a lot of breaks. What I'm getting at is we're not super concerned with how you perform when self-buffed, so long as you're functional. We're more concerned with how you perform when group buffed, since all of the most rewarding endgame content requires groups.

EDIT: We did not nerf Replenishment this patch. It has been lower, relative to LK, through all of beta.

Q u o t e:
Is it intended that our efficient heals only have about 20% more HPM than our big heals? Or should we expect those to be nerfed as well soon?

If healers stop casting the medium heals completely, then it's likely we nerfed them too far. Up until this change they weren't using the big heals enough.

We had the numbers set at what we thought made sense from a cost per benefit standpoint, but reality is always a little more complicated. Perhaps it was just easier using a single heal and being a B+ healer rather than having to worry about which of multiple heals to use in order to be an A+ healer.

Q u o t e:
Isn't this problem more due to:

a) the content being relatively easy on throughput, making players not require big heals, and
b) the current gigantic cost of the big heals making it impossible to tune encounters to require that throughput because healers run out of mana almost immediately if required to use those big heals?

The big heals get a decent amount of use, and they don't seem to run players out of mana unless the rest of the group is taking unnecessary damage (by say ignoring all the encounter mechanics because they can do so when running Heroic Nexus today).

If there's a heal we're worried about, it's the flash heals, but that's partially because so many of the talented or spec heals are also emergency heals that fill a similar niche -- things like Swiftmend, Penance and Holy Shock.