It’s a playstyle thing.

It has to do with Sombras spread leading her gun to being used more like a rapidfire shotgun. To use an example, at extreme close quarters, Zaryas laser would be horrible to use compared to D.va’s shotguns. D.va may not guarantee focused high damage, but her gun covers a wider area and guarantees a hit against fast targets or extremely close targets where you have to track quickly.

Sombra was commonly used (aside from EMP bot) as a backline harasser or assassin where she practically shoots point blank. If the target finds you out before you can finish them off (Thanks to the decloak noise), it’s down to you two bunnyhopping and circle straffing frantically trying to hit the other. Reaper has a better chance of killing you at this range than McCree. The one with the wider weapon spread wins in a nose to nose fight.

However, with emp nerf, the backline harassers are affected as well. I didn’t even think i would be affected because i don’t use EMP as much, but it did. I now use translocators offensively even more often than before (And i spent a lot of time in the backline back when emp bot was the norm). That means more time spent on roofs because i don’t leave it on healthpacks as much, and the 10% reduction was just enough to become consistent from that distance. Fights in tight quarters tho, took a bit of a hit.