Cleric healing vs sham/dru

Looking at spell lists it doesn't look like cleric healing varies too much from that of sham or dru. Is there something I'm missing? At what level do clerics begin to set themselves apart

While they share a lot of the same healing spells early on (and end up having more powerful spells at max level - complete heal, etc. depending on which expansion your TLP server is in), the difference begins at level 4 when clerics get Light Healing while druid and shaman get it at 9, and it just takes off from there.

So get the same heals but earlier and different spells in the end? I assume then most of this comes from complete heal?

Starting in Kunark Clerics get their own heals that are better than druid/shaman.
It only gets better from there, with heal over times, group heals, etc.

A Cleric can heal at double the potency of a Druid and Shaman with heals shared by the 3 classes. After level 30, when Clerics receive their own lines, they are even faster and more efficient as healers.

MGB Celestial to heal an entire raid? Youbetcha.

druid/shaman of equal level never get close to cleric healing power, be it lvl 5, 50, or 105

At level 30 clerics get first group heal, you dont have to target anyone making cleric super healers compared.

To start with, druids and shamans get the same heals, but slightly later. The slightly later is important - especially when the druid or shaman is in the levels just before getting an upgrade.

Then, clerics get complete heal. It's not actually that great when you first get it, because the tanks won't have enough HP to make it worth while, but it's still a staple 30 levels past getting it, which tells you something.

Druids and shamans get a big, 10 second heal, but they're nowhere near as good as complete heal.

In addition to the basic heal (light line) and complete heal, clerics also get fast heals (remedy line), heals over time (HoTs), group heals and group HoTs. The other classes (including paladins) get some of these, but no-one gets as big a heal as clerics at any one time, and no-one gets the full range of heals that clerics get.

Over-simplified yet accurate answer: Clerics range from 50% to 100% "better"healing depending on the level and expac.