Hmm, let's compare all the healing 2P T12 sets.
Holy Paladin:
Casting Flash of Light, Holy Light, or Divine Light on your Beacon of Light target has a 40% chance to grant you 2% of your base mana.
Holy/Discipline Priest:
Your Flash Heal, Heal, and Greater Heal spells cause you to regenerate 2% of your base mana every 5 sec for 15 sec.
Restoration Shaman:
Your periodic healing from Riptide has a 40% chance to restore 1% of your base mana each time it heals a target.
Restoration Druid:
Your periodic healing from Lifebloom has a 40% chance to restore 1% of your base mana each time it heals a target.
With that information let's see in my last log (Maloriak 25H) how those set bonuses are used.
I seem (Holy Paladin) to have healed my beacon 8 times with Divine Light,4 times with Holy Light and 0 times with Flash of Light
This would mean the bonus would have trigger 4-5 times, restoring 8-10% base mana.
Going to our Holy Priest, he seems to used Flash Heal, Heal, and Greater Heal all together 20 times.
This would restore 120% base mana. (If not overlapping each other)
Then our Restoration Shaman, his riptide ticked 305 times over the whole fight.
This means his set bonus triggered 122 times, restoring 122% base mana.
Last our Restoration Druid, his lifebloom ticked 404 times over the whole fight.
this means his set bonus triggered 161 or 162 times, restoring 161%-162% base mana.
TL;DR:
Maloriak 25HM - 10 Min Fight
2P T12 compared:
Paladin - Restored 8-10% base mana
Priest - Restored 120% base mana
Shaman - Restored 122% base mana
Druid - Restored 161-162% base mana