In my guild I almost always outheal the other healers on my resto druid, and not because they aren't good. They all couldn't believe that I am getting a buff next patch.
A large part of the problem for many resto druids is that they set themselves up for failure. You see many Resto druids on here with as little as 6k spirit, reforging it off their gear as if this was still the end of Cataclysm. Once they've got themselves to the point where they are so mana starved that they are afraid to actually cast spells, you see the associated bad advice begin to roll in. I see many throwing around the suggestion that you shouldn't rejuv a target until they already have a significant health deficit, as if the fact that a HoT is the absolute worst heal for that situation is no longer immediately obvious. And then they wonder why their HoTs get sniped?
Resto Druids are the best healers when we (surprise, surprise) focus on what we are good at; being able to lay a Blitzkrieg of HoTs down on the raid. No healer aside from maybe a disc priest can snipe a HoT that is already ticking on a target before they take damage. Our AoE throughput is actually quite amazing once you have rejuvs ticking on the people who need it.
Spirit is subjective you only need enough too heal the encounter i'm currently at 5k spirit and i don't have mana problems, but i only raid 10 man.
Spirit is subjective yes, but that's just silly.