This is a gross misrepresentation of the situation.
A GCD heal might suboptimal for your personal DPS while being optimal for the party's total DPS. This is the fundamental trade-off that a healer makes -- or would be making in this game if healing requirements were a bit higher and/or oGCD heals less available.
For example, presented with a situation where a party member has tanked the floor prior to a bona fide body-check mechanic, spending a GCD (or more) Raising that party member is the optimal thing to do. Continuing to blithely spam your nuke because "Raise is a DPS loss" is sheer idiocy given that doing so will lead to a wipe. In this situation, if you're the sort of healer that will cast that Raise only if it's "damage neutral", then to be blunt, you are a bad healer and should go play a DPS job.
The same style reasoning applies to every other GCD-based heal.