Qft!not At All True.
Battle Clerics (assuming A Clr18/ftr2 Level Split) Have Their Main Heal Spells Heal For The Following Percentage Of A Clr20's Heals:
Heal: 100%
Mass Cure Moderate Wounds: 93.75%
Mass Cure Light Wounds: 92%
Mass Heal: 90%
(whilst Less Often Used, The Other Healing Spells - Mass Cure Serious/critical Wounds, Cure Critical Wounds Etc All Have 94.7% Or Better Effect From A Clr18/ftr2; The Higher Level Mass Cures May Become More Useful In Future As More Players Get Access To Superior Devotion 8 Or Superior Ardor 8 Or Superior Efficacy 8)
That's *all* They Are Behind In Healing. Clr19/pal1 Builds Are Even Higher Healing.
And, With One More Person Doing Significant Melee Dps, Enemies Go Down Faster.
At Present Endgame, There Is *no* Quest Where I Would Rather Have A Ftr20 Max-dps Kensai Build And A Clr20 Healbot Build To Two Equivalently Geared, Well Built Clr18/ftr2 Builds. More Melee Dps, More Healing, More Bladebarriers (even If The Save Dc Is Lower Than That Of The Healbot), More Wipe Prevention (two People That Can Cast Quickened True Resurrection).