Basically what I'm trying to say is that I shouldn't have to rely on my pistol and 1v1. "I support you, why don't you support me?" That's the root of my frustration. But ya, when I hear genji ult, I instantly pull out my pistol, because I already know I'm about to take a sword slash to the dome. The amount of genji ults I've denied as Mercy is delicious.The most satisfying thing is killing a genji that thinks you're an easy kill. Just accept that your teammates are useless when it comes to protecting you and focus on keeping them alive so they absorb damage.
EDIT:
She released another video that focuses on 1v1's.
As soon as a Mei runs up on a teammate, I stop healing, pull out my pistol and start shooting, because unless they're a tank, they're dead anyway, and the next target is me. When I do this, usually one of two thing happens: 1) I deny them the kill because they're forced to iceblock, or 2) I deny them the kill because I kill them. There's also option 3, where they kill my teammate and then disengage or kill me, but that happens far less that the first two outcomes.