The whole healing-modelling gets even more interesting once one includes the different healing curves of the healers, and their different reaction abilities.
As a Shaman personally (and one constantly assigned to tankhealing), I will use a mix of Riptide, Lesser Healing Wave and Chain Heal as my go-to tankhealing spells. Depending on pace of damage and damage around the main tank.
However, since Riptide and CH supply me with a near-infinite amount of Tidal Wave charges I can and frequently will "spike" my healing into double hasted Healing Waves. Which drains mana fast, so I can't keep the maximum-output up for any extended stretch of time.
But I am able to supply 1,1s casting Healing Waves reflexively when I see a tank is still at non-full health after my last heal and I "feel" the next swing is incoming.
This is very different from a Paladin's output which is of equally distant spikes on both tanks. Mine is in smaller spiles but sometimes has more rare, really large spikes in it.
-- (The Death of Rats, Terry Pratchett, Soul Music)