Symmetra and Lucio are connected to each other via Vishka, on opposing sides, so yeah they're kinda self contained. Roadhog and Junkrat are Australian terrorists so idk. I always saw Zarya and Dva are symbols of the newer generation of would-be Overwatch agents, if the organization didn't collapse.
The thing about Sombra is, they've been teasing her in very deliberate ways. Documents on her in a stage on the same table as Soldier 76 (one of the files being Jack Morrison's real name to boot?), a sniper who is hiding her face, a sniper rifle which was prototyped within Overwatch during the time Anna was still at Overwatch, Anna being a sniper and the only original Overwatch agent who is "dead" and not accounted for? I don't see how it would be "random" at all since it's part of the tease.
The nature of Sombra's codename is definitely linked to Dorado, and she's definitely operating in that area for some story reason, but that's no reason to think it wouldn't be Anna with some personal agenda post-Overwatch. Worked out for Soldier 76 and Reaper after all.
