I've been doing my best to become much better with Sombra and some things are clicking especially juggling her abilities so I'm not vulnerable very often and I always have the jump on the other team.
Right now I just fought a team that was clearly in mic communication with each other and were grouped up behind their Reinhardt and bullying with their Dva, Mercy behind healing and powering up...
I found this is where I completely wrecked them. I would make sure whatever health packs near my team were hacked first so I could build ultimate quickly. I would hack the Dva and Rein, fight their Genji over health packs (he can't win) and Ult into their tight knit team and we would mow them down.
We had 3 healers (Mercy, Lucio, Ana) a Roadhog was our only tank.
They pushed close the last point finally as they were in communication with each other and they kept slightly adjusting to our loose plays but I found as often as I could keep harassing their Mercy and pulling down shields at the right time, they would eventually crumble. Their Genji had it out for me but as soon as he'd pull out his deflection, I'd hack him and dance over a hacked health pack to win. He learned to back off a bit after that.
It's been fun learning Sombra better lately.