Hmm those overheal numbers look pretty comparable, despite the extra damage and more healing required on average, I'd say. I just happened to press the GCD barrier more times, but still had less overheal with it. I imagine the 'overwritten' ones come from places like the Tracking Tremors (applying a new one before the stack mark takes the old one off) or the mit check right after the adds. Also:
Again, didn't use all of my everything, else my overheal would be even higher again.
Lastly, both me and my coheal in this run got purples on damage (me 81/them 94) and grey/green on healing (me 21/them 27). Could coordination/'synergy' be higher? Sure. But it was again a PF, and everyone just wants to get their reclears done and move on. Even so, I'd say that us both having sub-30 Healing parses means that we pretty effectively divided the healing requirements between us, but still, I had more in the tank that I could have used (which would have also ended up as overheal).