Healers have similar mechanic differences. There are mitigation healers, there are burst aoe healers, there are HoT healers, there are combo point healers. Beacon isn't similar to lifebloom, wild growth isn't like prayer of healing, prayer of mending doesn't compare to chain heal, and healing rain is nothing like holy radiance. Every healer has a unique set of tools (baring the three main heals which all serve different functions in different specs), and they feel pretty diverse. You should try playing more than healer class before assuming there aren't any differences.
the only thing I don't like the fact that every class is the same now.
One mana efficent heal.
One big heal.
One group heal.
One fast heal.
Cool?
homogenize much blizzard.
I miss wrath where pallys were primary tank healers, and other classes were primarily raid healers.