Tracer has more overall firepower and maneuverability than Sombra.
Sombra has more effective staying power and some level of zone control. She'll thrive on King of the Hill maps, but point control maps like Hanamura she tends to suffer.
Sombra's damage is among the lower end of the Offense class. Not as low as Genji's, but still fairly low. Her spread is worse than Soldier's, better than Tracer's. It is still very decent, however.
So,bea's ability to teleport anywhere on the map makes her quite dangerous and cunnin.e