It pretty much a given she will wreck a 3/3 setup. Heavy reliance on ability use in that comp.
She also wrecks comps that require a static defense or a defense that maximizes a choke point.
Surprisingly, the heroes that have the most to gain from Sombra are defense heroes, minus torb. Hanzo and WMs detection now have better utility in detecting her. Hacked bastion in turret mode can still shoot. Junkrat can trap/mine a lone translocator. Mei can spray around hoping to find cloaked sombras.
Thing is, Sombra's EMP is easily countered by EMP as well. So in a sombra vs sombra scenario...timing is everything or the first team to assassinate the other sombra first gets the edge.
In the end this is all just theorycrafting based on what we've heard. Need to actually play to really figure it all out.