Spoekes, I'll use LotA as an example. Though this goes for any fight. And also not just for healers. This happens with DPS as well.

I get within Shield Lob distance of KB. Due to lag, reflexes and movement I may very well hit face pull distance. As I was running, a healer tossed Medica 2 on the Party just to get ready for the floor DoT. Or a ranged DPS proceeds to unload into their rotation with damage buffs. Before I can get in position or even get more than Fast Blade off, KB has snacked on a Healer and is looking at either another healer or DPS. Voke, still try to get in position. But seconds after that Voke, someone else that has unloaded is going.

I know we don't have it here. But Sunders people!