So I also think it is simply a problem of the way the class is played.
Like that raid, I was Holy, other 4 healers were restro druids.
Druids use HOTs mostly, and if they keep applying it, everyone is healed quickly during low damage received times. A holy priest is not going to waste a healing spell on someone who is barely taking more damage than what they are healed.
So we have downtime until someone needs to be healed a lot. But even then, druids can get to that person quicker sometimes. So even if we cast our spell, by the time it goes off, that person may be fully healed. Therefore no healing counted.
So complaining to Holy about “not healing” when most of the raid is spent with everyone over 90% hp is stupid.
Basically druids may be healing all of the time while still doing damage. Holy priests will be jumping between healing and dps. So it is more spikes while druids are more a flat line.
Which will show on healing meters…and then people think the holy priest is not healing.