I have very similar experiences in the guild I'm in. I usually run with a druid/druid or druid/shammy. The RL recognizes pallies for superior MT/OT heals, and that's where I am generally assigned. The second the tank pulls the healing assignments go out the window. Druid is spamming everything he has on the entire raid, and generally I have overheal as high as 70% on some fights.

I agree that it's frustrating topping out the overheal meters. My numbers would be a lot better if I didn't have other people sniping heals on the tanks. The sad truth is if they want to do that, they can. The only real way I can get any "effective" heals in is to use FOL on the raid. Sometimes I beat the druid, but most of the time I don't.

I actually considered not healing at all to see if the druid would even notice. Maybe he just needs a mana nerf to keep him on his assignment =)

I've considered talking to the GM about the issue. If this druid can heal the entire raid all by himself they should just have me switch to my offspec and dps.